Marine fish case method: 50 questions

You keep a pair of ocellaris clownfish and three blue-green chromis in a 60 cm tank. A week ago you bought a blue tang at a shop and put it straight into the main tank without quarantine. At this morning's feeding, the tang has a dozen or so salt-grain-like white spots on its body and fins and is rubbing against the rocks. Two spots are also visible on a clownfish's tail fin. Temperature 25°C, specific gravity 1.023. Corals and an anemone share the tank.

Which is the most appropriate first action?

1. Add a commercial ich medication to the main tank at the labeled dose and treat everything
2. Move all fish to a quarantine tank, leave the main tank fishless for several weeks, and consult a shop or vet
3. Raise the water temperature to 30°C to kill the parasites and watch
4. Remove only the spotted tang and keep watching the other fish in the main tank

AnswerB. Move all fish to a quarantine tank, leave the main tank fishless for several weeks, and consult a shop or vet

ExplanationThe marine ich parasite leaves the fish, multiplies in the substrate and rocks, and reattaches. Treating only the fish leaves parasites in the tank, so the basic approach is to move all fish to a quarantine tank and leave the main tank fishless for several weeks to break the life cycle. Treat under the guidance of a shop or vet familiar with marine fish, and consult them the same day. Putting copper or similar medications into a main tank with corals and anemones kills the invertebrates, and live rock absorbs the medication so it does not work. 30°C is a dangerous temperature for marine fish and speeds up decline. Even if only some fish show spots, assume every fish in the same water is already infected and isolate them all.

IssuesThe biggest cause was adding the new fish directly to the main tank without quarantine. Ich is common in newly purchased fish, and a quarantine period would have kept it out of the main tank. The owner also did not understand that medications cannot be used in a coral tank.

ImprovementAlways quarantine new fish in a separate tank for 2–4 weeks before introduction. Keep a small quarantine tank, heater and air pump on hand, and check daily at feeding for white spots, gold-dust coating and breathing rate. In a coral tank medications cannot be used, so prevention is the only defense.

Sunday evening: two of the five anthias in a 90 cm tank are gasping near the surface, and their gills are moving too fast to follow. With the light at an angle, their bodies have a sheen as if dusted with fine gold powder, far smaller than ich spots. They ate normally until yesterday. Three days ago you added a wrasse bought at a different shop without quarantine.

What is the most appropriate response in this situation?

1. Suspect velvet, immediately move all fish to a quarantine tank, and urgently contact a vet who treats marine fish or a specialist shop
2. Treat it as mild ich and go to the shop for advice on your next day off next week
3. Stop feeding, lower the temperature by 2°C, and watch for a few days
4. Give the two coated fish a 30-minute freshwater dip and return them to the main tank

AnswerA. Suspect velvet, immediately move all fish to a quarantine tank, and urgently contact a vet who treats marine fish or a specialist shop

ExplanationA fine gold-dust coating with frantic gill breathing is typical of marine velvet (Amyloodinium). It parasitizes the gills, and the whole tank can die within days from respiratory failure, making it the most urgent disease. It falls under the manual's "call now" category: move all fish to a quarantine tank, leave the main tank fishless, and follow a specialist's treatment instructions. Mistaking it for ich and waiting until next week will be too late. Lowering the temperature does not remove the parasite, and withholding food only drains the fish's strength. A freshwater dip can temporarily knock off parasites, but 30 minutes is far too long and may kill the fish; never do it on your own judgment. Returning them to the main tank reinfects them.

IssuesBesides adding a new fish without quarantine, the owner did not know the difference between ich and velvet and could not judge the urgency. They also overlooked that anthias school, so one fish's problem spreads quickly to the group.

ImprovementLearn from photos to tell ich (salt-grain size) from velvet (extremely fine gold dust), and remember the latter is an emergency needing same-day action. Secure a quarantine tank and contact details for a marine-fish vet and shop in advance, with several options reachable on weekends.

Two blue-green chromis have been housed together for two months. The smaller one has been constantly chased and hiding behind rocks. This morning the smaller one has a red, raw ulcer on its flank, half its tail fin is missing, and one eye is slightly cloudy. It does not respond to food. Nitrate is over 50 mg/L and no water change has been done for a month. Temperature 25°C, specific gravity 1.024.

Which is the most appropriate first action?

1. Apply a human antibiotic ointment directly to the ulcer and return the fish to the main tank
2. Hope it heals naturally and keep the two fish together under observation
3. Isolate the ulcerated fish, do small daily water changes with clean seawater, separate it from its attacker, and consult a vet the same day
4. Change all the water in the main tank at once and stop feeding until the ulcer disappears

AnswerC. Isolate the ulcerated fish, do small daily water changes with clean seawater, separate it from its attacker, and consult a vet the same day

ExplanationFight wounds combined with high nitrate have very likely led to vibriosis. Ulcers, bleeding spots, cloudy eyes and loss of appetite together meet the threshold for a same-day consultation. First move the weaker fish to an isolation box to stop the attacks, do small daily water changes with clean seawater, and give antibacterial treatment only as directed by a vet. Human ointment damages the fish's slime coat and washes off immediately in water, so it has no effect. Keeping them together means continued attacks and a worsening ulcer. A full water change risks shock from the sudden change in water quality, and stopping food drains the strength needed for recovery.

IssuesDamselfish should be kept singly or in a large tank, yet two were housed together and the chased fish was left as it was. Going a month without water changes while nitrate was high invited bacterial infection.

ImprovementKeep damselfish singly, or if several, provide enough water volume and rock holes and introduce them at the same time. Test nitrate and pH weekly and make a 1/4 water change a habit. As soon as you spot a fish being chased, separate it with a divider or isolation box.

You notice several small white cauliflower-like growths on the dorsal fin of an ocellaris clownfish you have kept for two years. It eats normally, swims actively and still goes into its anemone. You recently moved house and relocated the tank, and nitrate tested slightly high at 40 mg/L. No other fish has lumps.

What is the most appropriate response in this situation?

1. Tear the lumps off with tweezers and wipe the area with antiseptic
2. Suspect lymphocystis, keep the water clean with water changes, reduce stress, and wait for it to resolve on its own
3. Assume a bacterial infection and dose the main tank with a commercial antibacterial at the labeled amount
4. Cull the fish and reset the tank before the infection spreads

AnswerB. Suspect lymphocystis, keep the water clean with water changes, reduce stress, and wait for it to resolve on its own

ExplanationWhite cauliflower-like lumps on the fins or body with appetite intact is typical of lymphocystis. It is viral and triggered by stress and poor water quality, but if the water is kept clean and stress reduced, it usually clears on its own in weeks to months. The move stress and rising nitrate are the cause, so repeated 1/4 water changes to bring nitrate down is the correct response. Tearing off the lumps opens wounds to bacterial infection. It is not bacterial, so antibacterials do not work and only degrade the water. Mortality is low, so culling is unnecessary. If it worsens so the mouth is blocked or the fish stops eating, see a vet within a few days.

IssuesOn top of the stress of the move, nitrate control afterward was lax. Faced with an unfamiliar symptom, the owner lacked the knowledge to judge urgency and considered the dangerous idea of physically removing the lumps.

ImprovementAfter major stress such as moving the tank or adding fish, increase water-change frequency for several weeks to stabilize water quality. Post a list of urgency levels for each symptom (spots, gold dust, lumps, ulcers) beside the tank, and when in doubt take a photo and consult a specialist shop or vet.

You have kept clownfish and damselfish in a 60 cm tank for six months. For the past few days their colors look dull overall, they spit out food after taking it, and they gather in a corner with clamped fins. Being busy, you have not changed water for a month and a half and have topped off evaporation with tap water. You have test kits but have not tested recently.

Which is the most appropriate first action?

1. Test nitrate, pH and specific gravity, and if abnormal, change 1/4 of the water with fresh seawater at the same temperature and specific gravity
2. Switch to a different food and try for a few days to see if appetite returns
3. Turn up the lighting and feed more often to perk them up
4. Drain all the tank water and replace it with new seawater

AnswerA. Test nitrate, pH and specific gravity, and if abnormal, change 1/4 of the water with fresh seawater at the same temperature and specific gravity

ExplanationDull color, staying still in a corner, spitting out food and clamped fins are the classic combination of weakening from nitrate buildup and falling pH. First test nitrate, pH (normal 8.1–8.4) and specific gravity; if abnormal, change 1/4 of the water with fresh artificial seawater matched for temperature and specific gravity, and repeat every few days to improve gradually. Changing the food ignores the cause, and feeding more raises nitrate further. Avoid a full water change, as the sudden change shocks the fish. If there is no improvement and they do not eat for several days or more, consult a vet who treats fish.

IssuesWater changes were neglected for a month and a half and there was no habit of testing the water. Topping off with tap water introduces chlorine and impurities, departing from the rule of topping off evaporation with RO water.

ImprovementFix weekly nitrate, pH and KH testing and a 1/4 water change on the calendar. Top off evaporation with RO or purified water and check specific gravity daily. Prepare for busy periods with an auto top-off or schedule, and track readings in a log.

7 a.m. on a weekday: every fish in the 90 cm tank is clearly moving its gills faster than usual, and several are swimming near the surface. No white spots or coating on the bodies. Last night you fed generously and leftover food remains on the substrate. The protein skimmer has produced no foam and been stopped for three days. Temperature 26°C. You have only 30 minutes before leaving for work.

What is the most appropriate action in the 30 minutes before work?

1. Judge it early ich and buy medication after work
2. Quickly feed them to check whether they perk up, then leave for work
3. Test ammonia, nitrate and specific gravity; if abnormal, change 1/4 of the water with seawater at the same temperature and specific gravity and add aeration
4. Since they look distressed at the surface, open the lid and point a fan at the water surface before leaving

AnswerC. Test ammonia, nitrate and specific gravity; if abnormal, change 1/4 of the water with seawater at the same temperature and specific gravity and add aeration

ExplanationWhen all fish breathe rapidly with no body-surface abnormalities, suspect water quality or oxygen shortage first. Leftover food and a stopped skimmer have most likely raised ammonia and depleted oxygen. As the manual says, immediately test ammonia, nitrate and specific gravity; if abnormal, change 1/4 of the water with fresh seawater at the same temperature and specific gravity and add aeration with an air pump. Siphon out the leftover food. If you assume ich and leave it until evening, they may be dead when you get home. Feeding increases ammonia. Leaving the lid open invites jump-outs, and a fan may cool the water too much.

IssuesThe stopped skimmer was left for three days, and feeding heavily in that state increased organic waste. There was no backup aeration or oxygen supply, and the owner tried to judge from symptoms without testing the water.

ImprovementCheck that the skimmer and pumps are running at each daily feeding and fix failures the same day. Feed only what is eaten within minutes and remove leftovers on the spot. Keep a spare air pump and artificial seawater on hand, and when something is wrong always go test, then water change, then oxygen.

A yellowtail blue damsel you have kept for a year has not responded to food for three days and stays inside a hole in the live rock. No white spots or ulcers, and breathing is calm. Nitrate 10 mg/L, pH 8.2, specific gravity 1.023, temperature 25°C, all normal. The clownfish tankmates are eating well. The damsel looks slightly thin.

What is the most appropriate response in this situation?

1. Since water quality is normal, stimulate appetite with frozen brine shrimp or similar, and if it still will not eat and keeps losing weight, consult a vet who treats fish
2. Move the rocks, catch the fish with a net, and push food into its mouth
3. Assume parasites are the cause of the poor appetite and add a dewormer to the main tank
4. Since water quality is normal there is no problem; leave it for as many weeks as it takes to eat

AnswerA. Since water quality is normal, stimulate appetite with frozen brine shrimp or similar, and if it still will not eat and keeps losing weight, consult a vet who treats fish

ExplanationThe manual says when a fish is not eating, first test the water; if normal, stimulate appetite with frozen or live food, and if it lasts 3 days or more and the fish is getting thin, see a vet who treats fish. Here three days have passed and weight loss is starting, so try frozen food while considering a visit within a few days. Chasing with a net damages the slime coat, and force-feeding is unrealistic for fish and worsens things through stress. Adding medication without a diagnosis harms filter bacteria and other fish, and there is no symptom to justify it. Leaving a thinning fish for weeks leads to death from wasting. Keep in mind internal disease or hidden fighting stress.

IssuesThe owner did not systematically work through the causes of not eating (water quality, disease, fighting, food preference) and was slow to notice weight loss. With no record of normal body shape or intake, changes could not be compared.

ImprovementNote each fish's intake and body shape at daily feeding, and set your own rule: 2 days without eating means test the water and try frozen food, 3 days means consult a vet. Find a vet who treats marine fish in advance and compile the information to bring (water volume, number of fish, specific gravity, temperature, nitrate, pH).

You keep six damselfish rather crowded in a 45 cm tank with only a hang-on filter and no skimmer. Today three of them have bodies that look cloudy white all over, as if coated in slime. Their gills are moving fast, and one is swimming unsteadily and has suddenly weakened. No ich-like grains are visible.

Which is the most appropriate first action?

1. Take the fish out and gently rub their bodies with your fingers to remove the slime
2. Suspect a body-surface parasite such as Trichodina, isolate the affected fish, and consult a specialist shop or a vet who treats marine fish the same day
3. Add double the labeled dose of ich medication to make sure it works
4. Clean the hang-on filter and watch for a week

AnswerB. Suspect a body-surface parasite such as Trichodina, isolate the affected fish, and consult a specialist shop or a vet who treats marine fish the same day

ExplanationA cloudy white, slimy-looking body surface with rapid breathing and rapid weakening is typical of Trichodina, with overcrowding and organic buildup in the background. Because it progresses fast, isolate the affected fish and consult a specialist shop or marine-fish vet the same day for treatment instructions. At the same time, test ammonia and nitrate and change water with clean seawater. Rubbing a fish's body with your fingers strips the protective slime coat and can be fatal. A double dose of ich medication risks killing the fish from toxicity, and it is the wrong disease anyway. Just cleaning the filter and waiting a week means the weakened fish die.

IssuesSix fish in a 45 cm tank is clearly overcrowded, and with no skimmer, organic waste built up easily. The owner lacked knowledge of how to distinguish this from ich and how fast it progresses, and tried to get by with equipment cleaning.

ImprovementKeep damselfish singly in 60 cm or larger, or with ample water volume if several. Add a protein skimmer to remove organic waste. Learn the differences and urgency of cloudiness, dust and spots on the body, and post the contacts of a specialist shop and vet reachable the same day beside the tank.

A clownfish that was observed in quarantine for two weeks before going into the main tank is, on day 5 after introduction, moving only one gill and rubbing its body against sand and rocks many times an hour. No white spots or coating are clearly visible. It still eats. Main tank water quality is normal, temperature 25°C. An anemone shares the tank.

What is the most appropriate response in this situation?

1. Since no spots or coating are visible, judge it normal and keep it in the main tank
2. Suspect gill parasites or early ich, return it to the quarantine tank for observation, and consult a shop or vet if it worsens
3. Assume the anemone's stinging cells are the cause and remove the anemone
4. Remove all rocks and substrate to stop the rubbing

AnswerB. Suspect gill parasites or early ich, return it to the quarantine tank for observation, and consult a shop or vet if it worsens

ExplanationMoving only one gill and rubbing the body are early signs of parasites on the gills or skin, and ich can start at a stage when spots are still invisible. This matches the manual's sign checklist, so the safe response is to return the fish to quarantine while it is still eating and watch for several days for spots or coating. If it worsens or spots appear, consult the same day. Judging it normal and leaving it lets the problem spread through the main tank. Clownfish live with anemones, so stinging cells are not the cause, and removal only takes away its home. Removing rocks and sand eliminates hiding places and increases stress.

IssuesTwo weeks of quarantine is the bare minimum and was short given the incubation period of ich. The owner used visible spots as the only criterion and dismissed behavioral signs like rubbing.

ImprovementMake 2–4 weeks the standard quarantine, and confirm there are no behavioral or breathing abnormalities during the final week before moving to the main tank. Observe and record behavioral signs daily, such as rubbing, one-sided gill breathing and clamped fins, for early detection.

The belly of a female ocellaris clownfish you have kept for three years has swelled over a few days. She spits out food after taking it and trails thin white feces. No ulcers or spots on the body, but her fin tips are slightly frayed and the area around the vent is red. Nitrate is high at 60 mg/L and no water change has been done for three weeks. The owner thinks she may be carrying eggs.

Which is the most appropriate first action?

1. Judge it a sign of spawning, increase feeding for nutrition, and watch
2. Press the belly gently with a finger to push the contents out
3. Isolate her, keep the seawater clean, and consult a vet who treats marine fish within a few days
4. Add a parasite medication found online to the main tank and wait a few days

AnswerC. Isolate her, keep the seawater clean, and consult a vet who treats marine fish within a few days

ExplanationA swollen belly, spitting food, white feces, a red vent and frayed fins point to a bacterial infection of the digestive tract (such as vibriosis) or internal parasites, promoted by the high nitrate. With spawning, appetite is usually unaffected and feces are normal. The correct response is to isolate her, keep the seawater clean, and get a diagnosis and treatment instructions from a marine-fish vet within a few days. More food burdens the gut and worsens the water. Pressing the belly damages internal organs and can be fatal. Adding medication without a diagnosis causes toxicity and delays diagnosis. If she worsens to lying on her side or breathing hard, switch to seeing a vet immediately.

IssuesNitrate was 60 mg/L with no water change for three weeks, and symptoms of illness were optimistically interpreted as spawning. The owner did not know digestive signs such as white feces and a red vent.

ImprovementKeep to weekly nitrate testing and 1/4 water changes, aiming for 20 mg/L or less. Observe feces color and shape daily as a health indicator. Before interpreting a symptom favorably, make it a habit to check it against the consultation guidelines (now, same day, within a few days).

The bubble-tip anemone that hosted your clownfish was ailing, so you moved it to another tank. Since the next day the clownfish has stayed inside a hole in the live rock, poking its head out only at feeding, and eats about half its usual amount. Body surface and breathing are normal and so is water quality. The tankmates are as lively as ever and show no sign of attacking the clownfish.

What is the most appropriate response in this situation?

1. Suspect disease, move it to a quarantine tank immediately, and give a medicated bath
2. Treat it as stress from losing its host, provide an alternative hiding place, maintain water quality, and observe for a few days
3. It hides because it misses the anemone, so put the ailing anemone straight back
4. Poke the hole with a stick to stimulate it out

AnswerB. Treat it as stress from losing its host, provide an alternative hiding place, maintain water quality, and observe for a few days

ExplanationClownfish use an anemone as home and safe zone, so losing the host makes them anxious, hide, and temporarily lose appetite. With body surface, breathing and water quality normal and the fish still eating a little, the sensible approach follows the manual's "an anemone or an alternative hiding place": provide a calm spot such as a pot or rock hole, keep the water clean, and observe for a few days. A medicated bath with no evidence of disease drains its strength. Returning the ailing anemone risks it disintegrating and fouling the water, and the fish may be stung. Poking with a stick adds stress and causes injury. If it eats nothing at all for 3+ days and gets thin, consult a vet.

IssuesNo substitute hiding place was prepared when moving the host, and the clownfish's behavior change was not anticipated. The root cause was poor anemone management, with the owner not grasping its light and flow requirements.

ImprovementIn a clownfish tank, always provide several refuges besides the host, such as pots and rock holes. Learn the anemone's light, flow and water requirements and catch early signs of trouble (shrinking, gaping mouth). Record behavior changes and check water quality and body surface first before judging.

After an ich outbreak you moved all fish to a quarantine tank and treated them for two weeks as instructed by a specialist shop. All spots on the fish are gone and they eat well. The main tank has been left fishless for two weeks with only corals. Managing the quarantine tank is a burden, and the owner wants to return the fish to the main tank this weekend. The main tank remains at 25°C.

What is the most appropriate decision in this situation?

1. Since the spots are gone, returning all fish to the main tank this weekend is fine
2. Leave the main tank fishless for several more weeks and confirm no recurrence in the quarantine tank before returning them
3. Raise the main tank to 30°C to kill the parasites in one go and return the fish the next day
4. Add medication to the main tank just in case, then return the fish

AnswerB. Leave the main tank fishless for several more weeks and confirm no recurrence in the quarantine tank before returning them

ExplanationAfter leaving the fish, the marine ich parasite survives in the substrate and rocks for several weeks. Even if the spots on the fish are gone, if the parasites in the main tank have not died out, the fish are reinfected the moment they return. As the manual says, the safe course is to leave the main tank fishless for several weeks (generally 4–6 weeks or more) and confirm no recurrence in quarantine before returning. Returning after two weeks is the most common relapse pattern. 30°C is dangerous for marine fish and bleaches corals. Medicating a main tank with corals kills invertebrates, and absorption into the rock weakens the effect. It takes effort, but keeping to the fallow period is ultimately the fastest solution.

IssuesThe owner did not understand the ich life cycle (leaving the fish and multiplying on the bottom) and mistook the disappearance of symptoms for a cure. There was no preparation to lighten the quarantine workload (auto feeder, simple water changes).

ImprovementTreat ich on two fronts, treating the fish and leaving the main tank fishless, and write both periods on the calendar at the start. Equip the quarantine tank with a heater, air pump and small filter so management can be sustained. Return fish a few at a time with the lights dimmed.

Day 3 after putting two blue devil damsels into a 60 cm tank. The larger one relentlessly chases the smaller one, whose tail fin is torn and whose flank has several scales missing, showing white. The smaller one swims shakily in a corner near the surface and cannot approach at feeding time. The owner has heard they will get used to each other eventually.

Which is the most appropriate first action?

1. Move the chased smaller fish into an isolation box first, and rearrange the rocks to reset the territory
2. They will get used to each other, so feed more and watch for a few days
3. Grab the two fighting fish bare-handed and pull them apart
4. Catch the aggressive larger one and put it in a small plastic case for a few hours as a time-out

AnswerA. Move the chased smaller fish into an isolation box first, and rearrange the rocks to reset the territory

ExplanationDamselfish are extremely territorial, and in a small tank the attacks continue until the weaker fish dies, so do not expect them to get used to each other. The manual says to isolate the chased fish first, rearrange the rocks to reset territories, and reintroduce simultaneously with the lights dimmed. Missing scales and torn fins are entry points for bacterial infection, so keep the seawater clean while the fins regrow. More food does not stop the fighting and fouls the water. Grabbing bare-handed injures both you and the fish through spines and bites. Removing the aggressor briefly does not change the territory, and attacks resume once it is back.

IssuesThe owner did not know the basic rule that damselfish are kept singly or in a large tank, and added two to a 60 cm tank at different times. No isolation box or divider was prepared, so there was no way to separate them immediately when fighting began.

ImprovementKeep damselfish singly as a rule; if several, introduce them simultaneously in a large tank. Keep an isolation box and divider on hand and separate fish the same day chasing begins. Decide in advance to consult a vet the same day if a wound ulcerates.

A carpet anemone added for the clownfish moved during the night and its tentacles touched a sleeping blue tang's flank. In the morning the tang has a white, raw-looking patch on its side and swims slightly tilted. Breathing is a little fast. The anemone is now spread wide near the pump intake.

Which is the most appropriate first action?

1. The white patch is ich, so add ich medication to the main tank
2. Anemone venom remains in the wound, so rinse the area with fresh water
3. Isolate the stung tang and observe in clean seawater, and secure the anemone's position and the intake
4. Grab the anemone bare-handed right away, peel it off the rock, and move it to the other side of the tank

AnswerC. Isolate the stung tang and observe in clean seawater, and secure the anemone's position and the intake

ExplanationWhen a non-host fish touches anemone tentacles, the stinging cells damage the skin, appearing as a white patch. The manual says to isolate and observe the stung fish, and if white patches appear, keep the water clean to prevent secondary infection. At the same time, if the anemone is sucked into the intake and disintegrates it contaminates the whole tank, so fit a sponge on the intake and adjust light and flow to guide it to a settled spot. The symptoms differ from ich, so medication is pointless and harmful in a coral tank. Rinsing with fresh water damages the slime coat and causes shock. Peeling an anemone off bare-handed tears its foot and kills it, and stings your hand too.

IssuesThe owner did not consider that anemones move, and housed one with a tang that is not a host species. The intake was unprotected and the risk of nighttime movement was not managed.

ImprovementSettle the anemone where light and flow suit it, and check the fish morning and evening while it is moving. Always fit a sponge on pump intakes, and avoid housing anemones with non-host fish. Keep an isolation box for injured fish and clean spare seawater on hand.

At night you hear a loud noise from the tank and find the stacked live rock has collapsed and the water is cloudy. One clownfish is pinned in a gap between rocks and cannot move; only its tail is moving. The other fish have scattered in fright. The rocks were not glued and were stacked directly on the sand. The owner panics and starts pulling all the rocks out.

Which is the most appropriate first action?

1. Grab the pinned fish by the tail and yank it out
2. Lift the rock gently so as not to crush the fish, free it, then check the fish for injuries and the water for cloudiness and quality
3. Take all the rocks out of the tank and leave the fish alone until the cloudiness settles
4. The cloudiness will weaken the fish, so do a full water change first, then rescue the fish

AnswerB. Lift the rock gently so as not to crush the fish, free it, then check the fish for injuries and the water for cloudiness and quality

ExplanationThe manual says after a collapse, lift the rock gently to free the trapped fish, then check for injuries and cloudiness. Pulling the fish damages scales and organs and cuts it on rock edges. Think about the order and lift rocks one at a time from the top. After the rescue, check for scrapes and bleeding; if injured, keep it in an isolation box with clean seawater. Removing all rocks eliminates hiding places, stirs up sand and stresses the fish further. A full water change shocks the fish, and the pinned fish dies from compression in the meantime. Let the filter and skimmer clear the cloudiness while waiting quietly, and test ammonia through the next day.

IssuesLive rock was stacked directly on sand without adhesive or reinforcement, easily toppled by digging fish. The owner did not know the collapse procedure and rushed to pull out all the rocks.

ImprovementPlace rocks on the bottom glass or a base and link them with aquarium adhesive or acrylic rods. If fish dig sand, keep sand out from under the rocks. Keep an isolation box and rubber gloves beside the tank for collapses or earthquakes, and share the procedure with the family.

At 11 p.m. you turned off the room light and tank light at the same time and heard a splash. Checking 20 minutes later, an anthias had jumped through a gap in the lid and lay limp on the floor, its body starting to dry, but its gills are moving slightly. A little dust is stuck to it. The startled owner picked the fish up.

Which is the most appropriate first action?

1. Rinse the fish under tap water to remove the dust before returning it to the tank
2. Since the body is drying, wrap it in a dry towel to warm it before returning it
3. Return it to seawater immediately, hold it in front of the flow so water passes through the mouth and gills, add slime-coat protectant at the labeled dose, and keep it dark and quiet for a few hours
4. A dried fish cannot be saved, so float it in the tank and watch until morning

AnswerC. Return it to seawater immediately, hold it in front of the flow so water passes through the mouth and gills, add slime-coat protectant at the labeled dose, and keep it dark and quiet for a few hours

ExplanationThe manual says if the gills move there is room for recovery: return a jumped fish to seawater immediately even if dry, pass water through the mouth and gills with flow, add slime-coat protectant at the labeled dose, and keep it dark and quiet for a few hours. Dust washes off naturally in seawater. Tap water destroys the slime coat through osmotic pressure and chlorine and is fatal. Wrapping in a towel dries it further and strips the slime coat. Giving up is premature; often the fish starts swimming after just being supported facing the flow. If it does not move after several hours back in the tank, or is still on its side the next day, that meets the "call now" threshold. Afterward keep the seawater clean so scrapes do not get infected.

IssuesAnthias jump when startled, yet the lid had a gap, and switching off the room and tank lights together created a sudden blackout. It took 20 minutes from hearing the noise to checking.

ImprovementCover the tank with no gaps and plug cable holes with sponge. Turn lights off in stages, e.g. tank light first with the room light on, then the room light a few minutes later. Check nighttime noises immediately, and keep slime-coat protectant and spare seawater beside the tank.

While rearranging rocks, a blue tang thrashed and the spine at the base of its tail hit your finger, causing a deep, bleeding cut. The owner is about to continue working with the hand still in the tank water. The hand also had a hangnail from three days ago. The tang fled behind the rocks but is uninjured. Half the work remains.

What is the most appropriate response in this situation?

1. Wash the cut in the tank water to stop the bleeding and continue working
2. Take your hand out of the water immediately, wash well under running water and disinfect; resume work only with gloves on, and see a doctor if it turns red and swollen
3. Seawater is antiseptic, so leave the cut and finish the work
4. Put an adhesive bandage on the cut and keep working bare-handed

AnswerB. Take your hand out of the water immediately, wash well under running water and disinfect; resume work only with gloves on, and see a doctor if it turns red and swollen

ExplanationA tang's tail spine is knife-sharp and causes deep cuts. Tank seawater contains nontuberculous mycobacteria and Vibrio, so the manual's instruction is to take your hand out immediately, wash under running water and disinfect. Resume work only with waterproof gloves, and if it becomes red, swollen, hot or slow to heal, see a doctor and mention the tank water exposure. Washing the cut in tank water pushes bacteria into the wound. Seawater is not antiseptic; it is the source of infection. A bandage peels off at once in water and is not waterproof. For the fish, check later that the thrashing did not injure it on the rocks.

IssuesUnaware of the danger of the tang's spine, the owner moved rocks bare-handed and worked in the tank with a hangnail. Working in a way that drove the fish made the tang thrash, endangering both person and fish.

ImprovementAlways wear rubber gloves for live rock work and keep hands out of the water when cut. Tell the family not to touch a tang's spine. For major rearrangements, move the fish to an isolation box first, and wash hands with soap afterward.

A clownfish whose tail fin was torn in a fight with a tankmate a week ago. You watched it in the main tank without isolating it, and now the tear is red and raw and the fin edge is eroding white. It eats but swims somewhat sluggishly. Nitrate 30 mg/L. The attacker still chases it occasionally. The owner had heard fins heal on their own.

What is the most appropriate response in this situation?

1. Fins regrow, so keep watching it in the main tank
2. Dab human antiseptic on the wound with a cotton swab and return it to the main tank
3. Keep it in an isolation box with clean seawater; since it has ulcerated, consult a vet the same day for antibacterial treatment instructions
4. Dose the whole main tank with antibacterial at the labeled amount and treat the attacker as well

AnswerC. Keep it in an isolation box with clean seawater; since it has ulcerated, consult a vet the same day for antibacterial treatment instructions

ExplanationA minor fin tear heals if you wait in clean seawater, but redness and an eroding edge are signs of ulceration from bacterial infection. The manual says if it ulcerates, start treatment, with antibacterials only as directed by a vet. First move it to an isolation box to stop the attacks, do small daily water changes with clean seawater, and consult a vet the same day. Left alone, the ulcer spreads to the body. Human antiseptic damages the slime coat and washes away in water. Antibacterials in the main tank kill filter bacteria, harm corals and anemones, and medicate fish that do not need it. Reset the attacker's territory by rearranging the rocks.

IssuesThe fin tear was dismissed; the fish was not isolated and was left for a week where attacks continued. Nitrate was also high, making the water prone to infection. The owner did not know the line between regrowth and ulceration.

ImprovementMove a fish injured in a fight to an isolation box the same day and let it recover in clean seawater. Learn that a red, white-eroding or spreading fin edge means ulceration, and make same-day consultation the rule. Change water to keep nitrate at 20 mg/L or less.

A blue-green chromis chased by a newly added wrasse crashed into a rock, and since the next day one eye is cloudy white and looks slightly bulging. It eats and breathes calmly. No ulcers on the body. Water quality is normal at nitrate 15 mg/L and pH 8.2. The wrasse still chases the chromis occasionally. The owner wonders about applying eye drops.

What is the most appropriate response in this situation?

1. Drip human eye drops into the fish's eye and return it to the main tank
2. Move it to an isolation box with clean seawater and rest, and consult a vet within a few days if it worsens or stops eating
3. The eye will not heal, so cull the wrasse that chases it
4. The cloudy eye is due to water quality, so do a full water change that day

AnswerB. Move it to an isolation box with clean seawater and rest, and consult a vet within a few days if it worsens or stops eating

ExplanationCloudiness in one eye after a collision is corneal trauma, and mild cases usually recover with clean seawater and rest. If the chasing continues it will crash again, so move it to an isolation box, maintain water quality and observe. If the bulging increases, both eyes become affected, it stops eating or ulcers appear, suspect bacterial infection (vibriosis) and see a vet within a few days. Human eye drops wash away instantly underwater and may contain ingredients harmful to fish. Culling the wrasse solves nothing; stopping the chasing by rearranging rocks or isolating comes first. Water quality is normal, so a full change is unnecessary and only adds stress from sudden change.

IssuesThe new wrasse was added later to a tank of territorial damselfish, and the chasing was left unaddressed. The number of hiding holes may also have been insufficient for the number of fish.

ImprovementWhen adding fish, dim the lights and rearrange the rocks to reset territories, making it close to a simultaneous introduction. Provide more hiding holes than fish, and if chasing persists, separate early with a divider. Check eyes and body surface at daily feeding.

A startled anthias crashed into a rock edge, leaving a cut about 2 cm long on its flank, with red blood trailing like a thread in the water. The bleeding continues after 5 minutes, and the fish rests quietly behind a rock. Breathing is slightly fast but the gills are moving. The owner is about to take the fish out and press on the wound to stop the bleeding.

Which is the most appropriate first action?

1. Take the fish out and press dry gauze on the wound to stop the bleeding
2. Pour hydrogen peroxide on the wound to disinfect it and return the fish to the tank
3. Let it rest in clean seawater, add slime-coat protectant at the labeled dose and observe; if bleeding continues or it ulcerates, consult a vet
4. Put the fish in fresh water until the bleeding stops, before bacteria get into the wound

AnswerC. Let it rest in clean seawater, add slime-coat protectant at the labeled dose and observe; if bleeding continues or it ulcerates, consult a vet

ExplanationThe manual's bleeding section says minor bleeding stops with rest in clean seawater, add slime-coat protectant at the labeled dose to prevent secondary infection, and if bleeding continues or ulcerates, see a vet who treats fish. Taking the fish out and pressing strips the slime coat and stops breathing, with no hemostatic benefit. Hydrogen peroxide damages fish tissue and causes shock. Fresh water destroys the slime coat osmotically and worsens bleeding. Rest it in an isolation box with reduced flow and darkness; if bleeding lasts over 30 minutes or the wound is red and spreading the next day, consult the same day. Afterward keep the water clean with small daily changes and wait for the fin and wound to heal.

IssuesIn a tank with easily startled fish like anthias, sharp rock edges had not been dealt with, and little care was taken over startling factors (sudden noises, lighting). The idea of taking the fish out of the water was dangerous.

ImprovementFile sharp rock edges round or reposition them, and ensure escape routes for fish. Avoid sudden noises and vibration around the tank and turn lights off in stages. Keep slime-coat protectant and an isolation box on hand, and tell the family the rule is never to take fish out of the water.

Trying to catch a clownfish for quarantine, you chased it with a net for over 10 minutes. You finally caught it, but its body got caught in the mesh, several scales came off, and a patch of slime coat peeled white. In the isolation box the fish breathes hard and is starting to lie on its side in a corner. The other fish are frightened and will not come out from the rocks.

What is the most appropriate response in this situation?

1. Keep the isolation box dark and quiet, run aeration, add slime-coat protectant at the labeled dose, and do not touch it until it moves
2. Gently remove the peeled slime coat with a finger, then let it rest
3. It looks distressed, so hurry it back to the main tank to be with its companions
4. Feed it right away to build its strength

AnswerA. Keep the isolation box dark and quiet, run aeration, add slime-coat protectant at the labeled dose, and do not touch it until it moves

ExplanationA fish whose slime coat and scales have been stripped by chasing and net abrasion weakens easily from extreme stress and oxygen shortage. The manual says keep it dark and quiet, maximize dissolved oxygen with aeration, add slime-coat protectant at the labeled dose, and do not touch it until it moves. Touching the peeled area spreads the damage. Returning it to the main tank leaves the reason for the chase unresolved, risks bacterial infection of the wounds, and exposes it to attack by other fish. A weakened fish cannot eat, and leftovers foul the isolation box water. Once swimming and breathing settle after a few hours, start small feedings the next day; if the wound turns red and raw, consult a vet the same day.

IssuesAgainst the basic rule of not chasing with a net, the owner spent over 10 minutes on the capture and exhausted the fish. They did not know how to catch with a container or trap and had no plan for the quarantine procedure.

ImprovementCatch fish with the lights dimmed when they are calm, using a clear container or a food-baited trap. If you must use a net, do not drive the fish into the rocks; combine it with a container underwater and finish quickly. Keep slime-coat protectant on hand and always rest the fish in the dark and quiet after capture.

Coming home, you find a small anthias sucked against the intake of a flow pump, its gill side pressed flat to the slits and unable to move. Its tail is still moving. The intake has no sponge or guard. The owner is about to peel the fish off with a finger. The clownfish tankmates are fine.

Which is the most appropriate first action?

1. Grab the fish's body and yank it off the intake in one pull
2. Switch off the pump to stop the suction, and if the fish does not come free on its own, gently detach it and observe it in an isolation box
3. Turn the pump to maximum to push the fish off with the flow
4. Leave the pump running and wait a few hours for the fish to free itself

AnswerB. Switch off the pump to stop the suction, and if the fish does not come free on its own, gently detach it and observe it in an isolation box

ExplanationFor a fish stuck on an intake, the first move is to switch off the pump to remove the suction. Once it stops, most fish come free on their own. If not, detach it gently underwater, move it to an isolation box kept dark and quiet with aeration, and check the gills and body for injury. Pulling it off while suction continues tears skin and gills. Increasing pump power increases suction, the opposite of what is needed. Left for hours, the fish suffocates from gill compression. After recovery, fit a sponge on the intake as the manual says before restarting. If white abrasions or ulcers appear, keep the seawater clean and consult a vet if it worsens.

IssuesNo sponge or guard was fitted on the intake, leaving the risk to small or weakened fish unaddressed. The owner did not know the basic step of stopping the pump in an emergency.

ImprovementFit sponges or mesh guards on every pump and skimmer intake and wash them weekly to prevent clogging. Reduce flow when small or weakened fish are present. Label the plugs so you know which to switch off in an emergency.

On a winter morning the tank glass feels lukewarm and the thermometer reads 31°C. The heater's thermostat apparently failed and stayed on. The clownfish and damselfish are breathing fast near the surface and the anemone has shrunk. Room temperature is 18°C. The owner is about to dump in a lot of ice to cool it down fast.

Which is the most appropriate first action?

1. Put ice straight into the tank and bring it down to 25°C in one go
2. Unplug the heater, increase aeration, and lower the temperature gradually over several hours, e.g. by floating frozen water bottles
3. Open the lid fully and add cold tap water, cooling it while quickly lowering specific gravity
4. Move the fish to a bucket of cold water and wait for the tank to cool

AnswerB. Unplug the heater, increase aeration, and lower the temperature gradually over several hours, e.g. by floating frozen water bottles

ExplanationFirst unplug the failed heater to remove the heat source. High temperature lowers dissolved oxygen and the fish suffocate, so increase aeration. Cool gradually over several hours, aiming for about 1°C per hour, by floating frozen water bottles or pointing a fan at the surface. Dropping ice in causes local rapid cooling, lowers specific gravity as it melts, and shocks the fish. Tap water is dangerous for its chlorine and the drop in specific gravity, and a fully open lid invites jump-outs. Moving fish to cold water is also temperature shock. The manual lists sudden temperature change from equipment failure under "call now", so contact a specialist shop or vet if the fish's breathing does not settle.

IssuesThe heater failure went unnoticed until morning, and the owner relied on a single heater with built-in thermostat. They did not know that rapid cooling is dangerous and had no procedure for temperature emergencies.

ImprovementUse a separate thermostat and heater or run two heaters, and add a safety thermostat that cuts off at an upper limit. Check the temperature daily and use a thermometer with an alarm. Keep frozen water bottles and a fan on hand, and remember to bring temperature back at about 1°C per hour.

Late at night, water is seeping from a crack that has run along a corner of the 90 cm tank, and the floor is wet. The water level has dropped about 2 cm in 10 minutes, and the power strip sits on the floor under the tank stand. There are six fish: clownfish, a tang and anthias. There is no spare tank, but you have a large bucket, a styrofoam box and an air pump.

Which is the most appropriate first action?

1. Safely cut power to the strip on the wet floor, transfer tank water to the bucket, and temporarily evacuate the fish with aeration
2. Seal the crack with waterproof tape, top up the water, and watch until morning
3. Drain all the water from the tank with the fish still in it and go buy a tank right away
4. Move the fish to a bucket of tap water, leave the tank as is, and wait until morning

AnswerA. Safely cut power to the strip on the wet floor, transfer tank water to the bucket, and temporarily evacuate the fish with aeration

ExplanationA leak with a power strip on the floor risks electric shock and an electrical fire, so first cut power safely at the breaker or wall outlet. Next transfer tank water to the bucket, evacuate the fish in that same water, secure oxygen with the air pump, and insulate with the styrofoam box or similar. In winter, keeping them warm matters. Waterproof tape cannot hold water pressure; if the tank fails overnight, over 100 L of water pours out and you lose fish and equipment. Draining the tank leaves the fish dry, and shops are closed. Tap water kills fish through chlorine and the difference in specific gravity. After evacuation, arrange a new tank and reuse the tank water and live rock to preserve the bacteria.

IssuesThe power strip was on the floor under the stand, an arrangement prone to electric shock in a leak. There was no spare tank or evacuation gear, and early signs of cracking were missed.

ImprovementMount the power strip above the tank's water level and make drip loops in cords so water cannot run along them. Keep a large bucket, air pump, insulation and spare artificial seawater for evacuation. Inspect the tank's silicone and corners monthly for clouding or cracks, and use an anti-seismic mat and dedicated stand.

A startled clownfish fled head-first into a narrow gap in the live rock and is wedged, unable to get out. Its tail fin moves but it cannot back out, and it has been stuck for over 10 minutes. The rocks are heavy and not easily moved. The owner is debating whether to pinch the tail and pull it out. Breathing is fast.

Which is the most appropriate first action?

1. Pinch the tail fin and pull it straight back with force
2. Wearing rubber gloves, gently lift or shift the rock forming the gap to create space for the fish to free itself
3. Wait for however many hours it takes for the fish to free itself
4. Pour food into the gap to calm the fish

AnswerB. Wearing rubber gloves, gently lift or shift the rock forming the gap to create space for the fish to free itself

ExplanationPulling a wedged fish makes its scales flare and come off, cuts it on spines and rock edges, and can damage internal organs. As with a collapse in the manual, the safe approach is to gently lift or shift the rock to create space and let the fish free itself. Protect your hands with rubber gloves and move rocks from the top down. Left too long, the fish weakens from compression and panic, and suffocates if gill movement is restricted. Food changes nothing and leftovers foul the water. After the rescue, check for scrapes and bleeding; if injured, keep it in an isolation box with clean seawater. Watch its swimming and breathing for anything abnormal through the next day.

IssuesThe rockwork left gaps narrower than the fish's body, creating a structure where a fleeing fish could get wedged. The rocks were heavy and unsecured, so they could not be moved in an emergency.

ImprovementBuild rockwork with passages wide enough for fish and hiding holes without dead ends, filling narrow gaps with coral sand or small stones. Link rocks with adhesive or rods while arranging them so they can be removed from the top in an emergency. Keep rubber gloves beside the tank and reduce startling factors (sudden lighting, vibration).

The float on the auto top-off failed, and overnight a large volume of RO water went in, nearly overflowing the 60 cm tank. Specific gravity has dropped from 1.023 to 1.015. The two clownfish are sitting on the bottom breathing fast. The anemone has shrunk dramatically. The owner is about to sprinkle salt mix straight into the tank to bring it back.

Which is the most appropriate first action?

1. Sprinkle salt mix directly into the tank and bring it back to 1.023 immediately
2. Move the fish at once into freshly mixed seawater at 1.023 to let them recover
3. Fish tolerate somewhat low specific gravity, so wait for evaporation to restore it naturally
4. Stop the top-off, increase aeration, and add concentrated seawater mixed in a separate container a little at a time, restoring specific gravity over half a day to a day

AnswerD. Stop the top-off, increase aeration, and add concentrated seawater mixed in a separate container a little at a time, restoring specific gravity over half a day to a day

ExplanationSudden changes in specific gravity put heavy strain on a fish's osmoregulation, and a rapid correction kills just as surely as a rapid drop. First stop the top-off, secure oxygen, and add small amounts of concentrated seawater fully dissolved and aerated in a separate container, returning to 1.023 over half a day to a day. Sprinkling salt mix directly creates local high concentrations and undissolved components that harm the fish and anemone. Moving them straight into normal-gravity water is a jump from 1.015 to 1.023, the same shock as the drop. Left at 1.015, the fish and anemone weaken, and evaporation takes days. After correction, watch breathing and appetite for several days and consult a specialist shop or vet if problems persist.

IssuesThere was no safeguard against a float failure (a top-off volume limit or timer control), and daily checks of specific gravity were not a habit. The owner did not know how important the speed of correction is.

ImprovementLimit the auto top-off reservoir to one day's volume and prevent overfilling with a timer or dual floats. Measure and log specific gravity at the same time daily, and adjust changes by about 0.001–0.002 per day. Always mix artificial seawater in a separate container and aerate for 24 hours before use.

While you were out, your 4-year-old tipped an entire container of pellet food into the tank. On returning, food floats on the surface and a large amount has sunk onto the substrate. The water is slightly milky, and the clownfish are pecking at the food but starting to breathe faster. It is about 50 times the usual twice-daily feeding. Temperature 25°C; filter and skimmer are running.

Which is the most appropriate first action?

1. The fish will eat it, so stop feeding for a few days and let them consume it
2. Stop the filter so the food is not sucked in, and leave it until morning
3. Change all the water to clear out the food
4. Remove as much floating and sunken food as possible with a net and pipette, test ammonia, change water with seawater at the same temperature and specific gravity, and keep testing for several days

AnswerD. Remove as much floating and sunken food as possible with a net and pipette, test ammonia, change water with seawater at the same temperature and specific gravity, and keep testing for several days

ExplanationLarge amounts of food rot quickly, sending ammonia and nitrite soaring and poisoning the fish. The manual names overfeeding as the main cause of rising nitrate, and physically removing the food is the top priority. Then test ammonia, change about 1/4 of the water with fresh seawater at the same temperature and specific gravity, and test daily for several days, repeating water changes as needed. Letting the fish eat it is the same as waiting for it to rot, and overeating also burdens the organs. Stopping the filter halts filtration and oxygen supply and makes things worse. A full water change shocks the fish and loses bacteria. If breathing does not settle, consult a specialist shop or vet.

IssuesThe food container was within the child's reach and the tank lid could be opened. There was no explanation to the family or physical safeguard against accidents while away.

ImprovementStore food, additives and medications in a lockable cabinet and use a locking lid on the tank. Set a rule that children feed only with an adult, using a small dedicated measuring spoon. Keep an ammonia test kit and spare artificial seawater on hand, and write out the emergency water-change procedure on paper.

During a water change, the moment you put your hand in the tank water you felt a tingling shock. A pump or the heater seems to have an electrical leak. The fish are a little restless and gathered behind the rocks. The power strip is on the floor behind the tank and shows marks where drips have landed. The owner is about to put a hand back in and touch each device to find the culprit.

Which is the most appropriate first action?

1. Without touching the water, switch off the circuit breaker or the wall outlet with dry hands, then inspect the equipment
2. Put on rubber gloves, reach into the water, and touch each device one by one to find the cause
3. It does not affect the fish, so put up with the tingling and finish the water change
4. Drain all the water from the tank and then inspect the equipment

AnswerA. Without touching the water, switch off the circuit breaker or the wall outlet with dry hands, then inspect the equipment

ExplanationElectrical leakage into water is a direct risk of electrocution and fire. First, without touching the water, switch off the breaker or the wall outlet with dry hands, then inspect each device with the power off. Rubber gloves have no guaranteed insulation and cannot be considered safe against leakage in water. Continuing while putting up with the tingling can affect the heart or cause a fall. Draining the tank kills the fish, and the shock risk remains if power is still on. Discard the leaking device, and on restoring power use a strip with a residual-current (GFCI) breaker, grounding and drip loops in cords to prevent recurrence. Fish can be weakened by weak current, so watch breathing and behavior after restoring power; if abnormal, change water and consult a specialist shop.

IssuesThe power strip sat on the floor where drips landed, with no residual-current breaker or grounding. Equipment was not inspected for wear, and the owner did not know the basic step of cutting power in an electric shock.

ImprovementMount the power strip on the wall above the tank, use one with a residual-current breaker, and ground it. Inspect heater and pump cords for damaged insulation every six months and replace old equipment early. Make it a habit to cut power before working, and label the plugs.

On a summer evening you come home to a silent tank: the pump, skimmer and chiller have all stopped. The power strip's safety cutoff apparently tripped. The temperature has risen to 29°C, the tang and anthias are gasping at the surface, and the water is slightly cloudy. How many hours it has been stopped is unknown. You have a battery air pump and ice packs on hand.

Which is the most appropriate first action?

1. Move the distressed fish from the surface into a bucket at once and cool them with ice water
2. The foul water is the cause, so do a full water change first
3. Restart all the equipment at once and check on the tank the next morning
4. First supply oxygen with the battery air pump; after restoring power, start the pump first, cool gradually with the chiller, and test ammonia

AnswerD. First supply oxygen with the battery air pump; after restoring power, start the pump first, cool gradually with the chiller, and test ammonia

ExplanationWith flow and oxygen stopped on top of high temperature, the fish are near the limit of suffocation. Supplying oxygen with the battery air pump is the top priority. Next identify why it tripped (overload or leakage), restore power, and start the pump and skimmer first to bring back flow. Lower the temperature gradually from 29°C with the chiller and ice packs, aiming for about 1°C per hour. Organic matter may have rotted while stopped, so test ammonia and if needed change 1/4 of the water with seawater at the same temperature and specific gravity. Rapid cooling with ice water is dangerous temperature shock. A full water change causes sudden change and loss of bacteria. Restarting everything at once risks tripping the strip again, and leaving it until morning without checking the fish is dangerous.

IssuesAll equipment was concentrated on one power strip, leaving the risk of overload unaddressed. There was no way to detect a stoppage (temperature alarm or power-failure alert), so the duration was unknown.

ImprovementSeparate life-support equipment (pump, aeration) from the chiller and lighting on different circuits with ample capacity. Learn of problems early with an alarm thermometer or smart-plug notifications. Keep a battery air pump and ice packs on hand, and put measures in place beforehand to keep summer temperatures below 28°C.

In a sump-filtered tank, the cover on the overflow pipe had been off for several days. This morning one small anthias is missing from the display and you find it swimming in the sump below. The sump is cramped and full of filter media. It has scrapes on its fins but can swim. The owner is chasing it around the sump with a net.

Which is the most appropriate first action?

1. The water quality in the sump is the same, so just keep it there
2. Chase it with the net, catch it, and return it to the display tank right away
3. Drain the sump and pick the fish up
4. Stop the sump pump, gently scoop the fish out with a container, refit the cover before returning it to the display, and watch the wounds

AnswerD. Stop the sump pump, gently scoop the fish out with a container, refit the cover before returning it to the display, and watch the wounds

ExplanationThe sump has strong flow and a pump intake, and a fish can be injured among the tightly packed media or sucked in. First stop the return pump to remove the flow, and, following the manual's capture rule, do not chase with a net but scoop gently with a clear container. Refit the overflow cover before returning the fish to prevent a repeat. Let the fin scrapes heal in clean seawater; if they turn red and raw, isolate and consult a vet. Keeping the fish in the sump is dangerous: no hiding places, the pump intake, and media maintenance. Chasing with a net strips the slime coat and weakens it. Draining the sump stops the display's filtration and may leave the fish dry.

IssuesThe overflow cover was left off for days and the risk of small fish falling in was dismissed. There was no habit of counting the fish daily, so the disappearance was noticed late.

ImprovementInspect the overflow cover and gaps weekly and replace them with ones that do not come loose. Count the fish at feeding, and if one is missing check the sump and floor immediately. Fit a sponge on the sump intake, provide a simple shelter there, and keep a clear capture container on hand.

On a summer night you sprayed insecticide for a few seconds to kill a mosquito in the room with the tank. The lid was open, and the skimmer's air intake is in the same room. 30 minutes later the clownfish and damselfish darted around frantically, then began to tip over on the bottom, breathing very fast. A thin oily film is visible on the surface.

Which is the most appropriate first action?

1. Insecticide breaks down quickly, so open the window and wait for the fish to settle
2. Move the fish to a bucket of tap water to wash off the chemical
3. Open the windows to ventilate, close the lid, skim off the film, change about 1/3 of the water with seawater at the same temperature and specific gravity, add activated carbon, and increase aeration
4. Turn the skimmer to maximum to remove the chemical in the foam

AnswerC. Open the windows to ventilate, close the lid, skim off the film, change about 1/3 of the water with seawater at the same temperature and specific gravity, add activated carbon, and increase aeration

ExplanationInsecticide ingredients (such as pyrethroids) are extremely toxic to fish; the airborne mist settles on the surface and also enters via the skimmer's air intake. First ventilate the room and close the lid to stop further contamination, blot the surface film with paper towels, change water with fresh seawater at the same temperature and specific gravity to dilute the chemical, adsorb it with activated carbon, and increase oxygen. Change water again after a few hours and observe through the next day. Waiting for it to break down only gives the fish time to die. Tap water kills fish through chlorine and the difference in specific gravity. The skimmer removes some film, but it draws in air and keeps pulling in the mist from the room. Several fish tipping over meets the "call now" threshold, so contact a specialist shop or vet.

IssuesUsing insect spray in the same room as the tank was the biggest mistake, and the open lid widened the damage. The owner did not understand that the skimmer draws in room air.

ImprovementAgree as a household never to use insecticide, air freshener, paint or tobacco smoke in the tank room. If unavoidable, seal the tank lid, stop the skimmer's air intake, and restart after ventilating. Keep activated carbon and spare seawater on hand, and write out the emergency water-change procedure on paper.

You mistakenly added the labeled dose of a copper-based ich treatment, meant for the quarantine tank, to the main tank with corals and shrimp. You noticed 5 minutes later. The shrimp suddenly stopped moving and the corals are starting to shrink. The fish are still swimming normally. You have activated carbon, 50 L of spare artificial seawater and buckets on hand.

Which is the most appropriate first action?

1. The fish are fine, so leave it and let the medication work
2. Give up on the corals and shrimp, prioritize treating the fish, and continue treatment in the main tank
3. Drain all the water and replace it with new seawater
4. Immediately evacuate the shrimp and corals to a container of medication-free seawater, and remove the drug from the main tank with large water changes, activated carbon and copper remover

AnswerD. Immediately evacuate the shrimp and corals to a container of medication-free seawater, and remove the drug from the main tank with large water changes, activated carbon and copper remover

ExplanationCopper is lethal to invertebrates such as shrimp, crabs, corals and anemones, and it adsorbs onto live rock and substrate, persisting for a long time. First evacuate the invertebrates into medication-free tank water (e.g. spare artificial seawater mixed with main tank water), then change as much of the main tank water as possible with seawater at the same temperature and specific gravity and remove the copper with activated carbon and copper remover. Repeat water changes over several days and, if possible, confirm the residual level with a copper test kit. Waiting kills the invertebrates for certain. Continuing treatment in a coral tank goes against the manual's rule of treating in quarantine, and adsorption onto the rock makes the dose unreliable. A full water change loses the filter bacteria, shocks the fish, and still cannot remove adsorbed copper.

IssuesMedications for quarantine and the main tank were kept together without distinction, and no check was made before dosing. The owner did not understand that copper is lethal to invertebrates and persists.

ImprovementStore medications only beside the quarantine tank and label containers clearly "NOT for main tank". Before dosing, say aloud which tank, which drug and how many mL. Keep activated carbon, copper remover and spare artificial seawater on hand, and designate an evacuation container for invertebrates.

You poured boiling water over a piece of live rock covered in button polyps (zoanthids) in the kitchen and scrubbed it bare-handed. Tens of minutes later, the owner developed a violent cough, shaking, headache and a bitter taste in the mouth. There is a small cut on a fingertip. The family thinks it is just a cold. The fish are fine.

What is the most appropriate response in this situation?

1. Suspect palytoxin poisoning, immediately open the windows and leave the kitchen, contact emergency services or call 119 (ambulance), and say you treated coral with hot water
2. Take cold medicine, lie down, and see how it is tomorrow
3. Go back to the kitchen, finish cleaning the remaining rock, then rest
4. Take a hot bath to sweat the toxin out

AnswerA. Suspect palytoxin poisoning, immediately open the windows and leave the kitchen, contact emergency services or call 119 (ambulance), and say you treated coral with hot water

ExplanationZoanthids contain palytoxin, an extremely potent poison, and the manual warns never to boil or pour hot water on corals or touch them bare-handed. Hot water carries the toxin in steam, which is inhaled, and it also enters through cuts. Cough, shaking, headache and a bitter taste are early signs of poisoning; severe cases cause breathing difficulty and cardiac effects, so ventilate, leave the area, contact emergency services or call 119 immediately, and be sure to state the cause (hot-water treatment of coral). Dismissing it as a cold and sleeping is the most dangerous choice, as symptoms can worsen rapidly. Continuing the work increases exposure. A bath worsens the condition and does not "sweat out" the toxin.

IssuesUnaware of the coral's toxicity, the owner used the worst combination, hot water and bare hands, in a poorly ventilated kitchen. The cut finger was also disregarded. The family did not know the danger and dismissed the early symptoms.

ImprovementNever dispose of zoanthids or palythoa by boiling, hot water or drying; seal them in a bag and dispose of them according to municipal instructions. Always do coral and live rock work with rubber gloves and safety glasses, outdoors or in a well-ventilated place. Share the presence of toxic organisms and their symptoms with the family.

Returning from a 3-night trip, the water in the 60 cm tank is slightly milky and smells fishy, and one damselfish is missing. Deep in the rocks you can see what looks like a white, bloated carcass. The two remaining clownfish are breathing fast and do not respond to food. The auto feeder ran as set. An ammonia test shows a clear reading.

Which is the most appropriate first action?

1. The carcass will decompose, so leave it and just watch the fish
2. Take out all the fish, empty the tank and clean it out
3. Add pH adjuster and deodorizer to remove the fishy smell
4. Remove the carcass, change 1/3 of the water with seawater at the same temperature and specific gravity, add aeration, and keep testing ammonia and nitrite for several days

AnswerD. Remove the carcass, change 1/3 of the water with seawater at the same temperature and specific gravity, add aeration, and keep testing ammonia and nitrite for several days

ExplanationA decomposing carcass releases large amounts of ammonia, poisoning the remaining fish. Ammonia damages the gills, and fast breathing with no response to food is that poisoning. First remove the carcass, change about 1/3 of the water with fresh seawater at the same temperature and specific gravity to dilute the ammonia, and secure oxygen with aeration. For the next several days test ammonia and nitrite daily and repeat water changes if detected. Feed sparingly until recovery. Leaving the carcass leaves the source of poison. Emptying and cleaning the tank wipes out the filter bacteria and ammonia rises again. pH adjusters and deodorizers only mask the cause, and a sudden pH change increases ammonia toxicity. If breathing does not settle, consult a specialist shop or vet.

IssuesThere was no arrangement to check on the fish during the 3-night absence, so the dead fish was left to rot. Checks of water quality and fish health before leaving may also have been insufficient.

ImprovementBefore a trip, test nitrate and pH and change water; reconsider the trip if a fish's condition is doubtful. While away, have family or a friend check the fish count and breathing once a day, or monitor remotely by camera. Set the auto feeder low and fix a routine of testing ammonia as soon as you return.

With badly chapped hands from winter dryness, you applied hand cream and sanitizer gel and immediately put your bare hands in the tank, spending about 10 minutes rearranging rocks. An oily film spread over the surface; afterward the clownfish began gasping near the surface and the damselfish started rubbing against the rocks. The skimmer is overflowing with foam.

Which is the most appropriate first action?

1. The film will disappear on its own, so leave it until tomorrow
2. The rubbing is ich, so add medication to the main tank
3. Wash your hands with soap, put them back in, and gather up the film by hand
4. Blot the film with paper towels, change 1/4 of the water with seawater at the same temperature and specific gravity, add activated carbon, increase aeration, and observe

AnswerD. Blot the film with paper towels, change 1/4 of the water with seawater at the same temperature and specific gravity, add activated carbon, increase aeration, and observe

ExplanationThe oils and chemicals in hand cream and sanitizer form a film on the surface that blocks gas exchange, and the ingredients irritate the fish's slime coat. Gasping is oxygen shortage, and rubbing is a reaction to skin irritation. First lay paper towels on the surface to blot the film, change water with fresh seawater at the same temperature and specific gravity to dilute the chemicals, adsorb them with activated carbon, and secure oxygen with aeration. Left alone, the film keeps oxygen low. Confusing it with ich and medicating harms the main tank's corals and bacteria without addressing the cause. Hands with soap residue add surfactant and make it worse. Always work with clean bare hands or rubber gloves.

IssuesThe owner did not consider that cosmetics and chemicals on the hands dissolve into the water, and worked bare-handed for a long time. They failed to reconcile winter chapped-hand care with tank work (using gloves).

ImprovementMake elbow-length rubber gloves the standard for tank work, especially when hands are chapped. When working bare-handed, use no cream, soap or sanitizer, and rinse well with water first. Keep paper towels for surface film, activated carbon and spare seawater on hand.

Late one January night, heavy snow caused a power outage. Room temperature has fallen to 12°C, and the 90 cm tank has dropped from 25°C to 22°C in three hours. Pump, heater and skimmer are all stopped and the fish sit still on the bottom. No word on when power will return. In the house you have a portable gas stove, blankets, styrofoam boards, a battery air pump and plastic bottles for warming.

Which is the most appropriate first action?

1. Secure oxygen with the battery air pump, cover the tank with blankets and styrofoam boards, float bottles of warm water to hold the temperature, and stop feeding
2. Boil water on the gas stove and pour it directly into the tank to restore the temperature
3. Move the fish to a small bucket and put it under the kotatsu (heated table) for warmth
4. Open the lid so the temperature does not fall, and put a space heater right beside the tank to warm the room

AnswerA. Secure oxygen with the battery air pump, cover the tank with blankets and styrofoam boards, float bottles of warm water to hold the temperature, and stop feeding

ExplanationIn a power outage, the priorities are oxygen and warmth. As the manual says, supply oxygen with the battery air pump, cover the tank with blankets and styrofoam boards to limit heat loss, and float bottles of warm water for gentle warmth. Stop feeding to avoid digestive problems and fouling the water. A gradual drop of 1–2°C can be tolerated for several hours, but below 20°C is dangerous, so check the thermometer often. Pouring boiling water in creates local hot spots and kills the fish. A small bucket or kotatsu causes rapid temperature swings and oxygen shortage. Opening the lid lets heat escape, and a heater right beside the tank heats one side of the glass and may crack it. When power returns, start the heater and pump first and check ammonia.

IssuesAlthough there were supplies for warmth and oxygen in a winter outage, the procedure for insulating the tank and using them was not worked out. The owner did not know the temperature limits in an outage and tended to reach for rapid heating.

ImprovementAssemble a battery air pump, insulation, bottles to use as hot-water bottles and a battery-free thermometer as an "outage kit". If you have a portable power station, decide the priority between heater and pump. In winter, attach insulation to the back and sides of the tank and keep the room from cooling.

At midday in August, the water in a 60 cm tank in a room without air conditioning has reached 29°C. You do not own an aquarium chiller. The tang and clownfish are breathing fast near the surface and the anemone has shrunk. Direct sunlight from the window falls on half the tank. In the house you have an electric fan, frozen water bottles and blackout curtains.

Which is the most appropriate first action?

1. Put in a large amount of ice directly and bring it down to 24°C in one go
2. Move the fish into seawater chilled in the refrigerator
3. Turn off the lights, shut the lid tight, leave the room and check tomorrow
4. Block the sun and turn off the lights, point the fan at the water surface, float frozen bottles, increase aeration, and lower the temperature gradually

AnswerD. Block the sun and turn off the lights, point the fan at the water surface, float frozen bottles, increase aeration, and lower the temperature gradually

ExplanationMarine fish enter the danger zone above 28°C, and high temperature also lowers dissolved oxygen, adding suffocation. First reduce heat sources by blocking direct sun with the curtains and turning off the lights, cool by evaporation with the fan on the surface, and float frozen bottles to lower the temperature gradually. At the same time increase aeration to secure oxygen. Aim for about 1°C per hour, and top off with RO water since evaporation raises specific gravity. Ice directly in the tank causes local rapid cooling and disturbs specific gravity. Moving fish into chilled seawater is temperature shock. A sealed lid prevents evaporative cooling, and leaving it until tomorrow kills the fish and anemone. In the long term, an aquarium chiller is essential.

IssuesThe basic rule that a chiller is a must in summer was ignored, and the tank was placed in direct sunlight. With no temperature alarm, the problem went unnoticed until 29°C.

ImprovementPlace the tank out of direct sunlight and install a chiller or cooling fan with thermostat before summer. On hot days leave the air conditioning on low, and use an alarm thermometer set to warn above 26°C. Always keep several frozen water bottles ready.

At night an earthquake of intensity 5-lower on the Japanese scale struck. About 1/4 of the water in the 90 cm tank spilled onto the floor, the live rock collapsed and clouded the water, and the heater has been pushed askew by a rock. Power is still on, but there is a puddle on the floor close to the power strip. The family is safe; aftershocks are possible. The fish are scattered in fright but swimming.

Which is the most appropriate first action?

1. Put your hands in the tank right away, restack the rocks, and calm the fish
2. Secure your family's and your own safety, check the power strip for water and cut power if needed, then check for trapped fish, leaks and the heater, and top up the water
3. Move all the fish to a bucket and evacuate them outdoors before aftershocks cause more collapse
4. Drain all the cloudy water, replace it with new seawater, and restack the rocks

AnswerB. Secure your family's and your own safety, check the power strip for water and cut power if needed, then check for trapped fish, leaks and the heater, and top up the water

ExplanationIn a disaster, human safety comes first, then removing the risk of electric shock and fire. If the floor water has reached the power strip, cut power with dry hands. Then check that no fish is trapped under the fallen rock and free any gently, inspect the heater's position and condition (running dry or cracked glass), and replace the lost water with seawater at the same temperature and specific gravity. Let the filter clear the cloudiness and test ammonia the next day. Putting your hands in to restack rocks while aftershocks are possible is dangerous, and hurried moves cause further collapse. Evacuating outdoors kills fish through temperature change and oxygen shortage. A full water change causes sudden change and loss of bacteria. Watch for jump-outs and injuries through the next day and consult if anything is abnormal.

IssuesThe live rock was unsecured and liable to collapse in an earthquake. The power strip was near the floor, creating a shock risk from spilled water. The heater was also inadequately secured.

ImprovementLink rocks with adhesive or acrylic rods and secure the tank with a dedicated stand and anti-seismic mat. Lower the water level a few cm so it spills less when shaken, and mount the power strip high on the wall. Use a heater with a guard, fixed with both suction cups and a bracket, and share the disaster procedure (people, then power, then fish, then water) with the family.

With a major typhoon approaching, the municipality has issued an evacuation order. Power and water outages may last 2–3 days. The 60 cm tank holds two clownfish and one damselfish. Pets are not allowed at the shelter. You can prepare two battery air pumps, spare batteries, insulation, a styrofoam box, plastic bags and 20 L of artificial seawater. You have two hours before leaving.

What is the most appropriate decision in this situation?

1. Put the fish in plastic bags, take them to the shelter, and manage them that way for 3 days
2. Feed them generously before leaving and leave the tank as it is until you return
3. Drain all the tank water, put the fish in a bucket, and keep them in the car trunk
4. Change water and stop feeding, run the battery air pumps, cover the tank with insulation, secure the lid and evacuate; check water quality and equipment as soon as you return

AnswerD. Change water and stop feeding, run the battery air pumps, cover the tank with insulation, secure the lid and evacuate; check water quality and equipment as soon as you return

ExplanationHealthy marine fish can tolerate a few days without food, but not oxygen loss or sudden temperature change. Before leaving, do a 1/4 water change to set up good water quality and stop feeding to prevent fouling. Secure oxygen during the outage with battery air pumps, soften temperature swings with insulation, and secure the lid to prevent jump-outs when equipment restarts after the outage. On return, test ammonia, temperature and specific gravity and confirm the equipment has restarted. Three days in plastic bags kills the fish through oxygen shortage and temperature change, and the shelter will not allow it either. Heavy feeding sends ammonia soaring. A car trunk gets hot and a bucket runs out of oxygen. There is no reason to drain the tank.

IssuesThe owner had not confirmed in advance that there was nowhere to take pets in a disaster and had no plan for managing the tank while away. They had battery air pumps but did not know the criteria for insulating and withholding food.

ImprovementDecide in advance on the policy of not moving the tank and getting through on oxygen and insulation. Assemble battery air pumps, spare batteries, insulation and lid clamps into a disaster kit. Line up fellow marine hobbyists or a specialist shop as an emergency boarding or advice contact, and write out the post-return check procedure on paper.

On a February morning the thermometer reads 19°C. The heater apparently failed and the temperature fell little by little overnight. Room temperature is 14°C. The clownfish sit still on the bottom with dull color, breathing slowly. You have one spare heater and can boil water. The owner is about to pour in hot water to get back to 25°C quickly.

Which is the most appropriate first action?

1. Install the spare heater, bring the temperature back to 25°C gradually at about 1°C per hour, add aeration, and hold off on feeding
2. Pour in hot water to reach 25°C in 30 minutes and feed right away
3. Set the spare heater to maximum, cover the tank with a blanket, and leave the room
4. Move the fish to a separate container warmed with hot water and heat them up quickly

AnswerA. Install the spare heater, bring the temperature back to 25°C gradually at about 1°C per hour, add aeration, and hold off on feeding

ExplanationAt low temperature the fish's metabolism has slowed, but rapid warming causes temperature shock and oxygen shortage. Install the spare heater, bring the temperature back to 25°C over several hours at about 1°C per hour, and secure oxygen with aeration. Hold off on feeding until metabolism recovers, then give small amounts from the next day. Pouring in hot water creates local hot spots that harm the fish and kills them through the sudden difference. Setting the heater to maximum and walking away leads to overheating and a high-temperature accident instead. Warming quickly in a separate container is the same shock. This meets the manual's "call now" criterion of sudden temperature change from equipment failure, so contact a specialist shop or vet if the fish lie on their side or breathe abnormally after rewarming.

IssuesIn winter the tank ran on a single heater with no backup. There was no temperature alarm, so the overnight drop went unnoticed until morning. The owner did not know how important the rewarming rate is.

ImprovementRun two heaters as the manual says, with enough capacity to hold a minimum temperature if one fails. Install an alarm thermometer and make morning and evening temperature checks a habit. Fix the rule of 1°C per hour for rewarming and cooling, and post the emergency procedure beside the tank.

A week ago you rearranged live rock bare-handed with a hangnail on your finger. A few days later the finger wound became red and swollen, a lump formed, and a red streak has gradually extended toward the wrist. No fever, but no sign of healing. The owner is applying an over-the-counter antibiotic ointment and watching. The fish in the tank are fine.

What is the most appropriate response in this situation?

1. Keep applying the over-the-counter ointment and watch for another week
2. You heard soaking in seawater heals it, so dip the finger in the tank water
3. Blame the tank, dump all its water and scrub it out
4. Suspect a nontuberculous mycobacterial infection or similar, see a dermatologist, and tell them you worked in a marine tank with live rock

AnswerD. Suspect a nontuberculous mycobacterial infection or similar, see a dermatologist, and tell them you worked in a marine tank with live rock

ExplanationTank seawater and live rock harbor nontuberculous mycobacteria and Vibrio, which enter through hand wounds and cause red swelling, lumps and infection spreading in streaks. The manual says to see a doctor if it turns red and swollen; ordinary antibiotic ointment does not work and diagnosis takes time, so see a dermatologist early and mention the marine tank and rock work to speed up the diagnosis. Watching with over-the-counter ointment lets it worsen and reach the joints and tendons. Dipping the finger in tank water introduces more bacteria. Resetting the tank is unnecessary; these bacteria are always present in tanks, and the countermeasures are gloves and hand washing.

IssuesThe owner did bare-handed live rock work with a wounded hand, and hand washing and disinfection afterward were inadequate. Not knowing this zoonosis and its early signs, they delayed seeing a doctor.

ImprovementMake rubber gloves mandatory for live rock work and keep hands out of the water when cut. Wash hands with soap after working. Share with the whole family: if a wound becomes red and swollen, forms a lump or spreads in a streak, see a doctor and tell them about the tank work.

A friend quitting the marine hobby gave you one ocellaris clownfish and two damselfish in a bag. The friend says one fish in their tank died recently of unknown cause. At home you have a main tank with five healthy fish, plus an empty 30 cm tank, a small heater and an air pump. The owner wants to acclimate them and put them straight into the main tank.

What is the most appropriate decision in this situation?

1. They look healthy, so acclimate them and put them straight into the main tank
2. Give them a 5-minute freshwater dip just in case, then add them to the main tank
3. Set up the 30 cm tank and quarantine them for 2–4 weeks, checking daily for spots, dust, breathing and appetite before introduction
4. Add a preventive medication to the main tank, then add the fish and watch

AnswerC. Set up the 30 cm tank and quarantine them for 2–4 weeks, checking daily for spots, dust, breathing and appetite before introduction

ExplanationFish from a tank where one recently died of unknown cause have a high chance of carrying ich or velvet. As the manual says, quarantine new fish in a separate tank for 2–4 weeks and check daily for white spots, gold-dust coating, cloudy skin, breathing rate and appetite before adding them to the main tank. With an empty 30 cm tank, heater and air pump available, a quarantine tank can be set up immediately using main tank water. Fish that look healthy may still be incubating disease. A short freshwater dip removes some parasites but cannot prevent incubating disease, and done by an inexperienced person it weakens the fish. Preventive medication in the main tank harms corals and bacteria with uncertain benefit.

IssuesThe owner was about to add fish from a tank with a death without quarantine, and had no plan to use the quarantine equipment they already owned. They also did not consider the risk of adding territorial damselfish to an existing group all at once.

ImprovementAlways observe new fish in quarantine for 2–4 weeks regardless of source. Keep the quarantine tank running at all times, or be ready to set it up instantly with main tank water and media. At introduction, dim the lights and rearrange the rocks to reset territories at the same time.

At the weekly water change you have been pouring the removed tank water and substrate debris down the kitchen sink, then washing vegetables in the same sink. Your 2-year-old has recently had repeated diarrhea and fever, and the doctor raised the possibility of food poisoning. You have sometimes prepared the child's meals with hands that had touched the tank water.

What is the most appropriate response in this situation?

1. The tank is unrelated, so keep the same habits and watch
2. Get rid of the tank and give up the fish
3. Disinfect the old tank water with bleach before pouring it down the sink
4. Dispose of tank water in the bathroom or outdoors, disinfect the sink, wash hands with soap after tank work, and tell the doctor you have an aquarium

AnswerD. Dispose of tank water in the bathroom or outdoors, disinfect the sink, wash hands with soap after tank work, and tell the doctor you have an aquarium

ExplanationTank water and substrate carry bacteria such as Salmonella, and the manual says not to pour tank water down the kitchen sink and to wash hands thoroughly. Dispose of tank water in the bathroom, toilet or outdoors, and disinfect the sink you have been using with kitchen bleach. Wash hands with soap after tank work and only then prepare food. Young children are prone to severe illness, so tell the doctor about the aquarium to help identify the cause. Giving up the tank is unnecessary; with changed hygiene practices it can be kept safely. Disinfecting the water with bleach still leaves the risk of sharing a food sink and is hazardous to handle. Changing nothing means it will recur.

IssuesThe habit of pouring tank water into the kitchen created a route for tank bacteria to reach food. Hand washing was not thorough, and the owner did not recognize the hygiene risk in a household with a toddler.

ImprovementFix the bathroom or outdoors as the disposal point for tank water, and dedicate buckets and hoses to the tank only. Enforce soap hand washing after tank work and a lid and placement that keep toddlers from touching the tank. Share a family rule of not handling food after touching the fish.

The net and pipette used to move fish in and out of the quarantine tank during ich treatment were also used as is to clean the main tank. The main tank holds five healthy fish and corals. A few days later, the tang in the main tank developed 2–3 white spots. The fish in quarantine are still under treatment, and the owner realizes the shared equipment may be the cause.

What is the most appropriate response in this situation?

1. Quarantine and treat all the main tank fish too, leave the main tank fishless, and keep equipment separate per tank, disinfected and dried
2. There are few spots, so leave the main tank fish as they are and just separate the equipment from now on
3. Add medication to the main tank and treat it together with the corals
4. Ich sometimes clears on its own, so feed more to build their strength

AnswerA. Quarantine and treat all the main tank fish too, leave the main tank fishless, and keep equipment separate per tank, disinfected and dried

ExplanationThe ich parasite travels between tanks on nets, pipettes and water droplets on hands. Once a main tank fish shows spots, assume every fish in that water is infected: as the manual says, quarantine and treat all fish and leave the main tank fishless for several weeks. Dedicate equipment to each tank, and after use rinse in fresh water and dry completely (the parasite is vulnerable to drying). Leaving it because the spots are few lets the parasite multiply on the bottom and spread to all fish. Medicating a main tank with corals kills corals and bacteria and is adsorbed by the rock. More food does not remove the parasite and fouls the water. Consult a specialist shop or vet the same day and make a treatment plan.

IssuesSharing equipment between the quarantine tank under treatment and the main tank created the infection route. The owner did not know that hands and droplets also transmit it, and had not extended the idea of quarantine to equipment.

ImprovementColor-code nets, pipettes, buckets, hoses and heaters for quarantine and main tank use and store them in separate places. Do quarantine tank work after the main tank and wash hands afterward. Rinse used equipment in fresh water and dry completely before storing.

At 9 p.m. a clownfish in the 60 cm tank is lying on its side on the bottom and does not flee from a finger, but its gills move slowly at a steady rhythm. At noon today you mixed artificial seawater on the strong side without measuring and did a 1/2 water change; specific gravity now reads 1.028 and the temperature is 23°C, 2°C lower than before the change. The other fish are also sluggish.

Which is the most appropriate first action?

1. A fish on its side cannot be saved, so take it out of the water to end its suffering
2. Hold the fish in your hand and move it through the water until it swims
3. Offer food to perk it up and see if it responds
4. While the gills still move, transfer it to a separate container of fresh seawater brought close to the original temperature and specific gravity, run aeration, keep it dark and quiet, and do not touch it until it moves

AnswerD. While the gills still move, transfer it to a separate container of fresh seawater brought close to the original temperature and specific gravity, run aeration, keep it dark and quiet, and do not touch it until it moves

ExplanationThe manual says that even on its side, if the gills move there is room for recovery; since chest compressions are impossible, move it to fresh seawater at the same temperature and specific gravity, maximize dissolved oxygen with aeration and flow, and keep it dark and quiet without touching until it moves. Here the cause is shock from the water change that sent specific gravity up sharply and temperature down, so prepare a separate container near the original 1.023 and 25°C and transfer the fish, while gradually bringing the main tank's specific gravity back down with RO water. Taking it out of the water is fatal, and it is not yet time to give up. Moving it by hand damages the slime coat and raises oxygen consumption. A weakened fish cannot eat and the food fouls the water. If it has not moved after several hours or is still on its side next morning, that meets the "call now" threshold; contact a specialist shop or vet.

IssuesThe water-change seawater was mixed without measuring specific gravity or temperature, and a large 1/2 change caused a sudden shift in water quality. When problems appeared, the owner did not suspect their own work as the cause and was slow to measure specific gravity.

ImprovementAlways match water-change seawater to the main tank with a hydrometer and thermometer, and aerate 24 hours before use. Make 1/4 the standard change and avoid large changes. Observe the fish for several hours after work, and fix the procedure of measuring specific gravity, temperature and ammonia first when something is wrong.

Coming home, you find an anthias that jumped through a gap in the lid lying limp on the floor. Its body is half dry and no gill movement is visible. You returned it to seawater right away, but it sank and lies motionless. The eyes seem to show a slight reaction. The owner is watching the clock, unsure how long to keep trying.

What is the most appropriate response in this situation?

1. Judge it dead since the gills are not moving, and remove it
2. Press the belly with a finger to push water in and out like artificial respiration
3. Hold it with its mouth facing the flow so water passes over the gills, add slime-coat protectant at the labeled dose, continue for several to ten-plus minutes, and once the gills start moving, rest it in the dark and quiet
4. Put it in fresh water so osmosis returns water to its cells

AnswerC. Hold it with its mouth facing the flow so water passes over the gills, add slime-coat protectant at the labeled dose, continue for several to ten-plus minutes, and once the gills start moving, rest it in the dark and quiet

ExplanationAs the manual says, resuscitating a fish is not chest compressions but pointing the mouth into the flow so water passes over the gills and supplies oxygen. Even a fish that stopped moving from drying may resume breathing after several to ten-plus minutes once water flows over the gills. Support the fish in aerated seawater, add slime-coat protectant at the labeled dose to protect the damaged slime coat, and once the gills start moving, leave it to rest in the dark and quiet without touching. Do not give up while the eyes still react. Pressing the belly damages internal organs. Fresh water destroys the slime coat and cells osmotically and is fatal. If the gills move but it is still not swimming the next day, that meets "call now": contact a specialist shop or vet. Afterward guard against infection of the wounds by keeping the seawater clean.

IssuesDespite knowing anthias jump, the lid had a gap, and there was no way to respond to a jump-out while away. Not knowing the resuscitation procedure (water over the gills), the owner nearly gave up as if it were cardiac arrest.

ImprovementCover the tank with no gaps and plug cable holes with sponge. Keep slime-coat protectant and an air pump beside the tank and post the jump-out procedure: return, flow over gills, dark and quiet. To reduce jump-outs while away, turn lights off in stages on a timer.

You are taking a clownfish with a spreading ulcer to a vet who treats marine fish, 40 minutes away by car. It is midday in midsummer and the car is hot. You have heavy plastic bags, a styrofoam box, rubber bands, ice packs and tank water. The owner plans to put the fish in a bag with just a little tank water and carry it on their lap.

Which is the most appropriate way to transport it?

1. Fill the bag completely with tank water, squeeze out the air, and carry it on your lap
2. Put it in freshly mixed artificial seawater in a clear container where it can be seen in the light
3. Put it in a container with a little tap water and place it in front of the car's air-conditioning vent
4. Double-bag it in tank water with plenty of air, put it in the styrofoam box with ice packs kept away from the bag, keep it dark, do not shake it, and keep the trip short

AnswerD. Double-bag it in tank water with plenty of air, put it in the styrofoam box with ice packs kept away from the bag, keep it dark, do not shake it, and keep the trip short

ExplanationThe manual's transport section says to double-bag in tank water with plenty of air, insulate in a foam box, keep dark, do not shake, and keep the trip short. The air is the oxygen supply; aim for 1/3 water and 2/3 air. In midsummer, put ice packs in the box without touching the bag to prevent overheating. Tank water is the water quality the fish is used to; new seawater differs in specific gravity and temperature and causes stress. Squeezing out the air causes oxygen shortage, and the lap transmits vibration that weakens the fish. A bright clear container frightens the fish, which thrashes and uses up oxygen. Tap water is fatal through chlorine and osmotic pressure, and air-conditioning airflow chills it rapidly. Bring notes for the vet: water volume, number of fish, specific gravity, temperature, nitrate and pH, introduction dates and medications used.

IssuesThe owner did not know the importance of oxygen (air volume), darkness and temperature during transport, and planned to use lots of water and carry it on the lap. Measures against the midsummer car temperature were also inadequate.

ImprovementPrepare a transport kit (heavy bags, rubber bands, foam box, ice packs and insulation, bottles of tank water). Record tank data routinely so notes for the vet can be made quickly. Confirm the route and clinic hours in advance, and in summer cool the car before setting out.

At 1 a.m. all eight fish in the 90 cm tank are crowded at the surface, gasping and breathing hard, and two are starting to tip onto their sides. No spots or coating on the bodies. You installed new equipment in the evening, and in handling the wiring the aeration tubing apparently came off. The skimmer is also running dry. Temperature 25°C, specific gravity 1.023.

Which is the most appropriate first action?

1. Reconnect the tubing, turn aeration to maximum, run the spare air pump too, change 1/4 of the water with seawater at the same temperature and specific gravity, and contact someone you can consult at night
2. Move all the fish to a small bucket and watch over them safely
3. Since it is the middle of the night, do nothing and consult the specialist shop first thing in the morning
4. Feed them to restore their strength and watch

AnswerA. Reconnect the tubing, turn aeration to maximum, run the spare air pump too, change 1/4 of the water with seawater at the same temperature and specific gravity, and contact someone you can consult at night

ExplanationSeveral fish breathing hard and tipping over at once is the most urgent state, classed as "call now" in the manual, and oxygen shortage is the most likely cause. First reconnect the tubing, turn aeration to maximum, and run the spare battery or other air pump to restore dissolved oxygen. Also consider contamination by organic matter or chemicals, change 1/4 of the water with seawater at the same temperature and specific gravity, and test ammonia. Contact a specialist shop, vet or fellow hobbyist available at night for advice. A bucket holds little water and runs out of oxygen quickly. Waiting until morning means most of them die. Food increases oxygen consumption and fouls the water. After recovery, watch breathing and body surface for several days.

IssuesAfter installing the new equipment, the wiring, tubing, aeration and skimmer were not checked. There was no way to detect falling dissolved oxygen, so discovery at night was delayed.

ImprovementAfter installing equipment or changing wiring, always visually confirm the aeration bubbles, skimmer foam and pump flow. Keep a spare battery air pump on hand and post nighttime emergency contacts (specialist shop, vet, fellow hobbyists) beside the tank. Decide in advance that several fish in trouble at once means immediate action.

At 10 p.m. the ulcer on a damselfish under treatment in an isolation box is oozing blood, with no sign of stopping after 30 minutes of watching. Breathing is fast but the gills move and it tries to swim upright. There is no after-hours vet for marine fish nearby, and your regular vet opens at 9 a.m. The owner is filming a video to ask for advice on social media.

What is the most appropriate decision in this situation?

1. Keep filming, wait for replies on social media, and follow their instructions
2. Rest it in clean seawater with slime-coat protectant at the labeled dose and darkness, watch mainly its breathing overnight, and compile the information and book a visit first thing in the morning
3. Dissolve a human hemostatic drug in the water
4. Take the fish out and keep pressing a cloth on the wound until the bleeding stops

AnswerB. Rest it in clean seawater with slime-coat protectant at the labeled dose and darkness, watch mainly its breathing overnight, and compile the information and book a visit first thing in the morning

ExplanationThe manual says minor bleeding stops with rest in clean seawater, add slime-coat protectant at the labeled dose to prevent secondary infection, and if bleeding continues or ulcerates, see a vet who treats fish. If the gills move and it can stay upright, reduce flow overnight, keep it dark and quiet, watch the breathing rate and whether it tips over, and see the vet as soon as the clinic opens. Compile water volume, number of fish, specific gravity, temperature, nitrate and pH, and medications used for the visit. Social media advice is of unknown reliability and wastes time, and filming frightens the fish. A safe dose of human hemostatic drugs for fish is unknown and may be harmful. Taking the fish out and pressing strips the slime coat and stops breathing. If it tips over or breathes hard during the night, contact your emergency contacts.

IssuesAlthough the ulcer could be expected to worsen, no nighttime contact or next-morning visit had been planned. In an emergency the owner turned to anonymous opinions rather than accurate information.

ImprovementPost the contacts of a marine-fish vet and a specialist shop or fellow hobbyist reachable at night beside the tank. On the day an ulcer or bleeding appears, decide to see the vet next morning if it worsens and compile the tank data. Keep slime-coat protectant and clean spare seawater on hand, and focus on observation at night.

You are taking a tang that has not eaten for three days and will not leave the rocks to a vet who treats marine fish. On the phone they asked for information about the tank, but all the owner could say was "about 60 cm, a few fish, and I change the water about once a month." You have test kits and a hydrometer but no records. The appointment is in two hours.

What is the most appropriate preparation in the two hours before the visit?

1. Just take photos of the fish and answer the rest from memory when asked at the clinic
2. Add a preventive medication to the main tank before leaving and tell them the name of the drug
3. Measure and record water volume, number of fish, specific gravity, temperature, nitrate and pH, introduction dates and medications used, and bring the fish in a bag of its own tank water
4. Rinse the fish in freshly mixed artificial seawater to clean it before taking it

AnswerC. Measure and record water volume, number of fish, specific gravity, temperature, nitrate and pH, introduction dates and medications used, and bring the fish in a bag of its own tank water

ExplanationThe manual's vet information section says to report water volume, number of fish, specific gravity, temperature, nitrate and pH, introduction dates and medications used, and to bring the fish in a bag of its own tank water. Most fish diseases stem from water quality and husbandry, so without these numbers neither a diagnosis nor a treatment plan can be made. In two hours you can test with the kits and hydrometer, calculate the volume from the tank dimensions, and note tankmates, introduction dates and recent changes (new fish, equipment, medications). Photos alone say nothing about water quality. Medicating just before the visit hinders diagnosis and harms corals. Rinsing in new seawater causes stress and sudden change, and loses the point of bringing tank water (diagnostic material).

IssuesThere was no habit of testing and recording water quality, and water changes at once a month were insufficient. The owner did not know what to tell the vet and, despite noticing the problem three days earlier, had not organized the information.

ImprovementUse a tank log or app to record weekly nitrate, pH, specific gravity and temperature, water-change volume, feeding, and the dates fish and equipment were added. Keep a vet-visit form beside the tank and write down symptoms daily from the day a problem appears. Confirm the contact details and hours of a marine-fish vet in advance.