Jellyfish case method: 50 questions

Sunday, 7 a.m. Two of three moon jellyfish kept for three months have their bells folded inward and are lying on the bottom of the kreisel tank, barely pulsing. Last night the owner mixed artificial seawater and immediately did a 30% water change. No hydrometer was used; the salt was measured as "the usual amount." The thermometer reads 20°C.

Which is the most appropriate first action?

1. Push the bells back upright with a pipette to restore their posture
2. Measure salinity and temperature; if off, correct them gradually over several hours
3. Turn the flow pump to maximum so the current spreads the bells
4. Assume underfeeding and add extra brine shrimp

AnswerB. Measure salinity and temperature; if off, correct them gradually over several hours

ExplanationBell inversion is a classic shock response to a sudden change in salinity or temperature, and when it appears right after a water change, a salinity mismatch in the new water is the most likely cause. Measure with a hydrometer first; if it is outside 1.021–1.024, correct it in small steps over several hours rather than all at once. Pushing the bell back with a hand or tool only tears tissue; posture will not return until the nerve net recovers. Stronger flow rubs the inverted bell against the bottom and walls and chips the margin. More food does not fix the cause, and uneaten food becomes an ammonia source. If it has not recovered after half a day or the bell starts to melt, contact a vet that treats invertebrates or the shop the same day.

IssuesArtificial seawater was mixed by eye without a hydrometer, and freshly mixed water with undissolved salt was added without matching the temperature. The owner did not understand that jellyfish are far more sensitive to water changes than fish.

ImprovementMix new water the day before and dissolve it with aeration; match salinity and temperature to the tank water before pouring gently. Use the hydrometer and thermometer at every water change and record the values in a logbook. Keep water changes to 10–20% weekly and never change more than 30% at once.

A weekday evening. Returning from work, the owner notices a moon jellyfish whose bell was 8 cm at purchase has shrunk to about 6 cm; the oral arms are shorter and the body more transparent. Being busy, the owner fed every other day, adding "roughly a spoonful" of hatched brine shrimp. They have never checked whether the stomach pouches color after feeding.

What is the most likely cause of the shrinkage, and what should be done?

1. Natural shrinkage from aging; just keep watching
2. Treat as disease and add a fish antibacterial medication to the tank
3. Suspect underfeeding; feed 1–2 times daily, confirm the stomach pouches color, and test the water
4. Downsize the tank to match the smaller body and raise the food density

AnswerC. Suspect underfeeding; feed 1–2 times daily, confirm the stomach pouches color, and test the water

ExplanationWhen underfed, jellyfish break down their own bodies and shrink (degrowth). In a young animal kept under three months and fed only every other day, underfeeding is the prime suspect. Feed newly hatched brine shrimp, rinsed in saltwater, 1–2 times daily and check that the stomach pouches (the four-leaf pattern in the center of the bell) turn orange after feeding. At the same time test ammonia and nitrite; if not zero, poor water quality may be suppressing appetite. Assuming aging and leaving it will let it shrink past recovery. Fish medications, especially copper-based ones, are lethal to invertebrates. A smaller tank destabilizes water quality and makes things worse. If shrinkage continues after two weeks of improved feeding, consult a vet that treats invertebrates or the shop.

IssuesThere was no habit of checking whether the animal was eating, and feeding amount and frequency were clearly inadequate. The owner took on the jellyfish without understanding that they need daily feeding.

ImprovementFeed 1–2 times daily, using orange-colored stomach pouches as the benchmark. Run two brine shrimp hatcheries so hatching never lapses, and measure and record the bell diameter with a ruler once a week.

Saturday afternoon. The day after adding extra brine shrimp "because they would enjoy it," the tank water is cloudy white and the three spotted jellyfish keep pausing their pulsing, drifting limply near the surface. One looks as if its bell margin is fraying. Uneaten food has accumulated in the sump.

Which is the most appropriate first action?

1. Test ammonia, siphon out leftovers, and do a 30% water change with water matched for salinity and temperature
2. Add activated carbon to the sump and wait a few days for the water to clear
3. Put an air stone in the tank and aerate strongly to clear the cloudiness
4. Remove all the jellyfish, empty the tank, wash it with tap water, then put them back

AnswerA. Test ammonia, siphon out leftovers, and do a 30% water change with water matched for salinity and temperature

ExplanationCloudy water, halted pulsing and a fraying bell margin are signs of ammonia poisoning from decaying excess food. First test ammonia and nitrite, siphon out all leftovers, and do a 30% water change with new saltwater matched for salinity and temperature. Retest the next day and repeat if needed. Activated carbon alone does not remove toxic ammonia, and the bells will melt while you wait. An air stone in the display tank is forbidden because bubbles collect under the bell and punch holes; aerate in the sump. Washing the tank with tap water leaves chlorine and fresh water behind and causes another shock, and the jellyfish get injured being cupped in and out. If pulsing does not return and melting begins, contact a specialist the same day.

IssuesThe owner believed more food was better and skipped siphoning leftovers 30 minutes after feeding. Leftovers in the sump were also ignored, and the owner did not know that in a jellyfish tank's small water volume ammonia reaches lethal levels quickly.

ImprovementFeed only enough to color the stomach pouches and collect leftovers with a pipette 30 minutes later. Wash the sump sponge weekly. Keep an ammonia test kit on hand and make it a habit to test whenever feeding changes or cloudiness appears.

A scorching August day. In a tank kept in a room without air conditioning, two spotted jellyfish that used to be brown have turned whitish and their bells have shrunk. The thermometer reads 30°C. The only lighting is a decorative blue LED on 4 hours a day. They are fed daily, but for the past few days the stomach pouches have colored only faintly and pulsing is weak.

Which is the most appropriate first action?

1. Bleaching means underfeeding, so increase brine shrimp to 3 times a day
2. Cool the water to 28°C or below with a fan or ice packs against the outside of the tank, and review the lighting
3. Drop ice straight into the tank to cool it fast
4. They can live without zooxanthellae, so turn off the lights and keep them quiet

AnswerB. Cool the water to 28°C or below with a fan or ice packs against the outside of the tank, and review the lighting

ExplanationBleaching in spotted jellyfish is the loss of their symbiotic zooxanthellae due to high temperature or insufficient light, and 30°C is in the danger zone. First cool the water gradually to 28°C or below with a cooling fan, an aquarium chiller or ice packs against the outside of the tank. Then run a full-spectrum white LED 8–10 hours a day so the zooxanthellae can photosynthesize. Keep feeding. Ice dropped into the tank creates pockets of fresh water and sharp temperature differences that invert or melt the bell. More food alone does not address bleaching and leftovers foul the water. Zooxanthellae species weaken steadily without light, so turning off the lighting is wrong. If color does not return and shrinkage continues after two weeks, consult a specialist.

IssuesTropical, zooxanthellae-dependent spotted jellyfish were kept in a room with neither temperature control nor suitable lighting. The owner did not know that a decorative blue LED is insufficient for photosynthesis and had made no preparations for summer heat.

ImprovementInstall a cooling fan or chiller before summer to keep zooxanthellae species at 24–28°C. Run full-spectrum LED lighting on a timer for 8–10 hours. Check the thermometer daily and start cooling immediately on any day above 28°C.

A moon jellyfish kept for six months has had a ragged, chipped bell margin for several days, with spreading cloudy-white patches. The tank walls have a brown biofilm and the bell occasionally touches the intake mesh. Ammonia is undetectable, but no water change has been done for a month.

Which is the most appropriate response?

1. Trim the chipped parts with scissors to tidy the shape
2. Remove the wall biofilm, adjust the flow so the bell no longer hits the intake, and resume water changes
3. Ammonia is zero so water quality is fine; just watch
4. Add a fish slime-coat conditioner at double the recommended dose to heal the bell

AnswerB. Remove the wall biofilm, adjust the flow so the bell no longer hits the intake, and resume water changes

ExplanationA chipped, cloudy bell margin is physical abrasion combined with bacterial growth. Even with zero ammonia, a month without water changes lets nitrate and organics build up, and wall biofilm is a bacterial breeding ground. Scrape the walls, adjust the flow so the bell rotates gently in the center without touching the intake, and resume 10–20% weekly water changes. Cutting the bell with scissors widens the wound and worsens infection and fluid loss. Judging water quality by ammonia alone is a mistake. Fish additives have no established safety in invertebrates, and a double dose is more dangerous still. If the melting spreads from the margin toward the center of the bell, contact a specialist the same day.

IssuesThe owner assumed zero ammonia meant safety and neglected water changes and wall cleaning. The flow design was poor, and the bell was left repeatedly striking the intake.

ImprovementPut 10–20% weekly water changes on a fixed schedule and remove wall biofilm weekly. Observe the flow daily to confirm every animal is rotating gently in the center. Test nitrate monthly as well, so water quality is judged by several indicators.

Spring. White dot-like polyps had been multiplying on the tank walls and were ignored; one morning dozens of tiny jellyfish a few millimeters across are swimming. The three moon jellyfish are healthy, but the water is slightly cloudy and a trace of ammonia is detected. The tank is a small 15 L kreisel, fed once daily.

Which is the most appropriate response?

1. Move the juveniles to a separate container, clean the polyps off the walls, and restore water quality with a water change
2. The juveniles will die on their own, so leave them
3. Drop the water temperature by 10°C at once to kill the juveniles
4. Move only the adults to another tank and dry out the original tank for a full reset

AnswerA. Move the juveniles to a separate container, clean the polyps off the walls, and restore water quality with a water change

ExplanationMoon jellyfish have a polyp stage that attaches to the bottom and walls, and triggers such as temperature change cause strobilation, releasing juveniles (ephyrae). It is not a disease, but sudden overcrowding in a small tank raises leftovers and ammonia and leads to water-quality accidents for the adults. Move the juveniles to a separate container with a pipette, scrape the polyps off the walls, and do a water change with matched salinity and temperature to bring ammonia back to zero. Left alone, competition for food and water quality weakens everyone. A sudden temperature drop shocks the adults too. Drying out the tank is extreme; the adults are injured in the move and the filter bacteria are lost. If you want to raise the juveniles, set up a dedicated container.

IssuesThe owner regarded the wall polyps as mere dirt and left them, not knowing the jellyfish life cycle. They did not understand how fragile a small tank is, where overcrowding sends ammonia soaring.

ImprovementClean walls and bottom weekly and remove polyps as soon as they appear. If you want to raise juveniles, prepare a separate container and feeding plan. Test ammonia weekly as routine, and always test when the number of animals increases.

Two upside-down jellyfish kept for one month. Brine shrimp are added from the top of the tank daily, but the owner has never once seen the stomach pouches turn orange after feeding. Both sit on the bottom; the bells pulse but the oral arms are retracted. The flow is on the strong side and the food is immediately swept to the intake.

Which is the most appropriate first action?

1. Not eating means disease, so give a medicated bath with a broad-spectrum fish remedy
2. Pause the pump at feeding time and deliver food near the oral arms with a pipette to confirm they eat
3. Increase the food fivefold so the whole tank is full of food
4. Sitting on the bottom is abnormal, so keep lifting them by hand until they swim

AnswerB. Pause the pump at feeding time and deliver food near the oral arms with a pipette to confirm they eat

ExplanationFor upside-down jellyfish, sitting inverted on the bottom is the normal posture; they catch food with the oral arms facing up. With strong flow, food is swept to the intake before it reaches the oral arms, so daily feeding ends up as no feeding. At feeding time stop the pump for a few minutes, slowly release food near the mouth with a pipette, and check that the stomach pouches color. If they eat, it is a husbandry problem and weaker flow solves it. A medicated bath has no basis without disease and its safety for invertebrates is unknown, so it is dangerous. Five times the food sends ammonia soaring from leftovers. Lifting a bottom-sitting animal by hand causes stress, bell damage and stings. If they still do not eat after a week of changes, consult a specialist.

IssuesThe owner did not understand the normal posture and feeding mechanism of upside-down jellyfish and did not judge flow strength by how the food moved. There was no habit of confirming feeding by the color of the stomach pouches.

ImprovementMake it standard to pause the pump at feeding and deliver food near the oral arms. Set the flow to the minimum at which upside-down jellyfish sit stably on the bottom. Check stomach-pouch color at every feeding and feed non-eaters individually.

The week the owner switched artificial seawater brands, four moon jellyfish began pulsing weakly and one shrank and sank to the bottom. The new water was at 1.023 and the temperature was matched, but it was added right after the salt was stirred in. Test kits show zero ammonia and nitrite; pH has not been measured.

What is the most likely cause, and what should be done?

1. Suspect shock from undissolved salt or a pH shift; redo the water change in small amounts with water mixed and aerated the day before
2. The brand does not suit them, so do a full water change with the old brand right away
3. More food will restore them, so double the feeding
4. Moon jellyfish are hardy, so just watch for a week

AnswerA. Suspect shock from undissolved salt or a pH shift; redo the water change in small amounts with water mixed and aerated the day before

ExplanationRight after mixing, artificial seawater has undissolved salt and an unstable pH and ion balance, and jellyfish react more sensitively than fish. A pH difference is especially likely when changing brands. The remedy is to use stable water mixed and aerated the day before, match salinity, temperature and pH to the tank water, and redo the water change in small amounts spread over several days. A full water change is the greatest possible shock and will certainly worsen the sunken animal. More food does not relieve water stress and increases leftovers. "Hardy, so leave it" means it is too late once the bell starts melting. Isolate the sunken animal in stable water in a separate container, and consult a specialist if pulsing has not returned after a day.

IssuesThe owner did not know the importance of dissolving and maturing artificial seawater and added freshly mixed water. There was no habit of measuring pH; water quality was judged only by salinity and ammonia. The impact of a brand change was underestimated.

ImprovementMix artificial seawater the day before and aerate it overnight outside the sump. Add a pH test kit and check salinity, temperature and pH before every water change. When changing brands, shift the mixing ratio gradually over several weeks and avoid abrupt switches.

Three newly acquired upside-down jellyfish have not settled on the bottom after two days; they are being swept around the tank and bumping into the walls. The flow is still at the "moon jellyfish" setting. The lighting is a dim blue LED and the water is 22°C. One bell margin is starting to chip. The bottom is bare clear acrylic with no decor, and they are fed daily.

Which is the most appropriate response?

1. Set the flow to minimum, raise the temperature to 25–28°C, switch to bright white lighting, and give them a bottom they can settle on
2. They want to swim, so increase the flow further for exercise
3. Press the bells onto the bottom with tweezers to make them settle
4. Turn the lights off completely to calm them

AnswerA. Set the flow to minimum, raise the temperature to 25–28°C, switch to bright white lighting, and give them a bottom they can settle on

ExplanationUnlike moon jellyfish, upside-down jellyfish naturally attach inverted to the bottom and photosynthesize with zooxanthellae. At a moon jellyfish flow setting they cannot settle, get swept into the walls and chip their bells. Set the flow to minimum, provide a flat bottom, raise the temperature to 25–28°C for this tropical species, and run a full-spectrum white LED 8–10 hours a day. Stronger flow is counterproductive and worsens the damage. Pressing with tweezers tears the bell and stings the keeper. Turning off the light causes loss of zooxanthellae and bleaching. If they settle within a few days of correcting the environment, there is no problem; if they still have not settled after a week and keep shrinking, consult a specialist.

IssuesThe owner introduced a different species without researching species-specific needs, leaving the moon jellyfish settings in place. They did not grasp the basics that upside-down jellyfish are tropical and need light and a flat bottom.

ImprovementBefore acquiring a new species, confirm its temperature, flow, lighting and bottom requirements and prepare a separate tank or change the settings. Make separate tanks for separate species the rule, and record posture and bell condition daily for the first week.

One of three moon jellyfish kept for two months developed cloudy white spots on the bell a few days ago; they are spreading and the tissue around them is slightly slack. The other two are normal. Water tests show zero ammonia, salinity 1.022, 20°C, but the sump has never been cleaned since purchase.

Which is the most appropriate response?

1. Remove and dispose of the spotted animal to prevent spread
2. Suck off the cloudy areas with a pipette to clean them
3. Isolate the spotted animal in a separate container of clean saltwater, and clean the sump and change water in the main tank to reduce the bacterial source
4. The spots are a change in pattern, so do nothing

AnswerC. Isolate the spotted animal in a separate container of clean saltwater, and clean the sump and change water in the main tank to reduce the bacterial source

ExplanationCloudy white spots and slack tissue on the bell are signs that bacteria or similar agents are starting to damage it; left alone, the spots develop into holes and the bell melts. The cause is usually bacterial growth on organic matter accumulated in the sump and on the walls. Move the affected animal to a separate container of clean saltwater at matched salinity and temperature and let it rest, and improve the main tank by washing the sump sponge and changing water. Disposal is premature; bell damage often regenerates in good water. Sucking the spots with a pipette punches holes in the bell. Dismissing them as a pattern change lets them spread. If the spots keep spreading or shrinkage continues 2–3 days after isolation, consult a specialist.

IssuesThe owner assumed zero ammonia meant perfect water and neglected sump cleaning for two months. They noticed the bell change but lost several days to "wait and see," and had no isolation container ready.

ImprovementSchedule sump sponge washing every two weeks and wall cleaning weekly. For any cloudiness or spots on the bell, set up an isolation container the same day and photograph the progression. Keep a small isolation container and spare saltwater on hand.

Three moon jellyfish arrived by mail order and were poured into the tank immediately after opening the bag, without checking the bag's temperature. An hour later two bells are folded back and one animal keeps pausing its pulsing and has sunk to the bottom. The bag water felt cold to the touch; the tank was 22°C. The bag water went into the tank too, and salinity was not measured.

What is the most appropriate action to take now?

1. They are already in, so nothing can be undone; feed them and wait for recovery
2. Stop the flow and pump, and raise the heater to 25°C quickly to warm them
3. Lift the sunken animal to the surface by hand and make it swim
4. Reduce the pump, check salinity and temperature, keep them quiet, and watch for pulsing to recover over several hours

AnswerD. Reduce the pump, check salinity and temperature, keep them quiet, and watch for pulsing to recover over several hours

ExplanationMoving them abruptly from a shipping bag chilled in transit into a warm tank causes a double shock of temperature and salinity, inverting the bell and halting pulsing. Once they are already in, the best course is to avoid any further change. Set the pump to minimum so the flow does not abrade the bells, confirm the tank's salinity and temperature are in range, and quietly watch for pulsing to recover over several hours. Do not feed; they will not eat during shock and leftovers foul the water. Rapid heating causes another shock. Lifting a sunken animal by hand does not restore posture, damages the bell and stings the keeper. If pulsing has not returned after half a day and the bell begins to melt, contact the seller the same day.

IssuesThe owner did not know acclimation was necessary and added the bag water, chilled in transit, without measuring it. They had no understanding that jellyfish are even more sensitive to temperature and salinity changes than fish.

ImprovementOn arrival, float the sealed bag in the tank for at least 30 minutes to equalize temperature, then add tank water to the bag a little at a time over an hour to bring salinity closer. Transfer with water in a cup and do not put bag water in the tank. Skip feeding on arrival day.

Two moon jellyfish kept for over a year have gradually shrunk over the past month and their oral arms have shortened. They are fed twice daily and the stomach pouches color. Ammonia and nitrite are zero, salinity 1.023, 20°C, and weekly water changes continue. Pulsing is still regular.

Which is the most appropriate judgment?

1. If rechecking water quality and feeding shows no problem, regard it as age-related decline; maintain the environment and observe
2. Drop the temperature sharply to force rejuvenation before the end of life
3. Shrinking is disease, so give a medicated bath with a fish antibacterial
4. Increase feeding to 5 times a day to restore body size

AnswerA. If rechecking water quality and feeding shows no problem, regard it as age-related decline; maintain the environment and observe

ExplanationThe adult lifespan of a moon jellyfish is usually a few months to a year; even under proper care, the bell shrinks and the oral arms shorten as the end of life approaches. If water quality, salinity, temperature and feeding are all correct and the stomach pouches color, age-related decline is the reasonable conclusion. Forced intervention only shortens life further. A sharp temperature drop causes shock and halts pulsing. Antibacterials, especially copper-based ones, harm invertebrates and there is no evidence of disease. Feeding 5 times a day does not stop aging and raises ammonia from leftovers. Maintain a stable environment, and isolate the animal for the sake of the others once the bell begins to melt. If polyps are on the walls, raising the next generation is an option.

IssuesThe owner's husbandry was appropriate, but they did not know that jellyfish are short-lived and age-related shrinkage is unavoidable, so there was a risk of panicking at "shrinking = abnormal" and intervening.

ImprovementCheck each species' lifespan when acquiring them and plan on decline at around one year. Distinguish aging by rechecking water quality and feeding, and record bell diameter in a logbook. Learn polyp management to raise the next generation.

9 p.m. Top-up water for evaporation was poured in forcefully from a hose, spreading fine bubbles through the tank. Several silvery bubbles are stuck under the bells of two moon jellyfish, which are tilted and floating near the surface as if pulled upward. They are pulsing but cannot ride the current. The third is circling normally.

Which is the most appropriate first action?

1. Pause the flow and gently draw off the bubbles with a pipette
2. Poke the bells with a finger to dislodge the bubbles
3. Turn the flow to maximum to blow the bubbles off
4. The bubbles will disappear on their own, so leave them until morning

AnswerA. Pause the flow and gently draw off the bubbles with a pipette

ExplanationBubbles trapped under the bell are the most common cause of jellyfish injury; left alone, they push the tissue apart and punch holes, and their buoyancy presses the animal against the surface where the bell dries and breaks down. Pause the flow to settle the animal, bring the tip of a pipette or dropper close and draw off only the bubbles. Poking with a finger tears the bell and gets you stung. Stronger flow does not dislodge bubbles and slams the bell into the walls and intake. Left until morning, holes are very likely. Even if a hole forms, it usually closes within days if water quality is kept optimal, so stay calm and focus on water quality. If the hole widens and the bell begins to melt, consult a specialist.

IssuesThe owner poured top-up water forcefully, unaware that bubbles are a physical weapon against jellyfish. Rushing a nighttime task, they skipped the basic step of pouring gently.

ImprovementPour top-up and change water gently down the wall from a cup or hose end held near the surface. Always check for bubbles under the bells after adding water. Use fresh water for top-ups to prevent salinity rise, and consider an auto top-off unit.

During the morning check, a hole about 5 mm across is found near the center of one moon jellyfish's bell. Last night a sump pipe came loose and bubbles flowed into the display tank. The edges of the hole are not cloudy. Pulsing is regular and the other animals are fine.

Which is the most appropriate response?

1. Add a fish slime-coat conditioner to the tank to close the hole
2. Take it to an aquarium for surgery
3. Scoop the animal out with a net into a separate container and observe
4. Fix the pipe to stop the bubbles, keep water quality optimal, continue feeding, and let it heal naturally

AnswerD. Fix the pipe to stop the bubbles, keep water quality optimal, continue feeding, and let it heal naturally

ExplanationA jellyfish bell regenerates well, and a bubble hole usually closes within days to a week if water quality is good. With no cloudiness or melting around the hole and regular pulsing, the best course is to repair the pipe that caused it, stop the bubbles, keep water quality optimal with water changes and leftover removal, keep feeding and wait for recovery. Fish slime-coat conditioners have unknown safety in invertebrates and do not close holes. This is not a surgical case, and the stress of transport would do more harm. Netting tears the bell further; moves are always done with water in a cup, and here no move is needed. If the edge of the hole turns cloudy white and spreads, or shrinking begins, contact a specialist the same day.

IssuesThe sump plumbing was poorly secured, a structural weakness that let bubbles flow into the display tank. The setup made it impossible to notice equipment trouble overnight.

ImprovementSecure pipe connections with cable ties and design the return to the display tank so it enters below the surface without introducing bubbles. Inspect the pump and plumbing weekly. Photograph bell injuries so recovery can be compared over time.

On returning home, one spotted jellyfish is found pinned by its bell against the tank intake, unable to pulse. The intake mesh had come off. Part of the bell appears drawn into the intake holes and the margin is starting to turn white. The others are swimming normally. It is unknown how long it has been stuck.

Which is the most appropriate first action?

1. Grab the bell by hand and pull it off in one go
2. Stop the pump immediately and pour water over it, waiting for it to release on its own
3. Leave the pump running and wait for the jellyfish to free itself
4. Remove the entire intake fitting and pull the jellyfish out

AnswerB. Stop the pump immediately and pour water over it, waiting for it to release on its own

ExplanationA jellyfish stuck on the intake is an emergency: as long as the pump runs, the bell keeps being drawn in and tearing. First stop the pump to remove the suction, then pour water from a cup toward the bell or reverse the flow and let it detach naturally. Pulling by hand rips off large pieces of the bell and stings the keeper. Waiting with the pump running spreads the damage. Removing the intake fitting yanks the animal and tears it just the same. After release, even a torn bell often recovers if the mouth and stomach remain and water quality is maintained. Refit the mesh and adjust the flow so the bell cannot be sucked on before restarting the pump.

IssuesThe owner had not noticed the intake mesh was off, and the pump flow was strong enough to pin a jellyfish. A mesh-covered intake is an essential feature of a jellyfish tank, and checking it had been neglected.

ImprovementUse a double layer of fine mesh on the intake, fix it so it cannot shift, and add it to the daily check. Set the pump flow to the minimum at which a bell near the intake is not drawn on. Make it a habit to check the pump and intake before going out.

To clean the tank, the owner scooped a moon jellyfish with a fish net into a bucket; the bell caught in the mesh and about a third of it tore. The bucket holds freshly mixed tap water and salt mix. The jellyfish is still pulsing, but the torn section flutters in the current and the owner is unsure whether to return it to the tank.

What is the most appropriate action to take now?

1. A torn animal cannot be saved, so dispose of it
2. Stick the torn section back together with tape or glue
3. Cup it into a separate container of tank water, keep water quality optimal, let it rest, and continue feeding
4. Return it to the original tank and increase the flow to spread the bell

AnswerC. Cup it into a separate container of tank water, keep water quality optimal, let it rest, and continue feeding

ExplanationNetting a jellyfish lets the bell catch in the mesh and tear. But even with a large piece of bell missing, it can regenerate and recover as long as the mouth and stomach remain. First, transfer it with water in a cup into a separate container filled not with freshly mixed seawater but with tank water of stable salinity and temperature. Keep the flow at minimum or off, let it rest, and keep feeding to maintain strength. Disposal is premature. Glue or tape destroys tissue and fouls the water. Returning it to the tank and exposing it to strong flow widens the tear and injures the others. If shrinkage continues and melting begins after three days, consult a specialist.

IssuesThe owner did not know the basic rule that jellyfish must never be handled with a net. Using freshly mixed artificial seawater as the destination exposed an injured animal to additional water-quality shock.

ImprovementAlways move jellyfish with water in a cup or bowl. When moving is needed for cleaning or water changes, prepare a container of tank water set aside in advance. Keep nets away from the tank and store jellyfish-only tools together on a dedicated tray.

At morning feeding, two of a moon jellyfish's four oral arms are found torn to about half length. Yesterday a small decorative coral rock was placed in the tank. The jellyfish is swimming but seems unable to carry food to its mouth, and the stomach pouches do not color after feeding. Fragments of white mucus cling to the rock's edges.

Which is the most appropriate response?

1. Remove the decoration, assist feeding by delivering food directly to the mouth with a pipette, and wait for regeneration
2. Stop feeding to let the body rest until the oral arms regenerate
3. Trim the torn oral arms with scissors to match the remaining length
4. It cannot live without oral arms, so dispose of it

AnswerA. Remove the decoration, assist feeding by delivering food directly to the mouth with a pipette, and wait for regeneration

ExplanationThe oral arms carry food to the mouth, and they were likely torn by rubbing on the decoration's edges. Oral arms regenerate in days to weeks, but catching food is difficult meanwhile. Remove the decoration immediately, pause the pump at feeding time, gently release food near the mouth with a pipette and confirm the stomach pouches color. Stopping food starves the regeneration of energy and shrinkage begins. Cutting with scissors adds wounds and causes infection and fluid loss. Disposal for lost oral arms is wrong; regeneration can be fully expected. Keep water quality optimal, and consult a specialist if the stomach pouches still do not color and shrinkage continues after a week.

IssuesA decoration was added for display, breaking the rule that nothing with edges goes in a jellyfish tank. The injury was noticed only the next day, and the decoration that caused it stayed in overnight.

ImprovementPut nothing but jellyfish in the tank. Install heaters and air stones in the sump. If you want decoration, do it outside the tank or on the background. Add oral arm and tentacle length to the daily check and record changes.

A winter night. A small heater for spotted jellyfish had been placed on the bottom of the display tank. On returning home, one animal is found pressed bell-first against the heater surface, motionless, with the contact area turned white. The heater is running and the water is 26°C. The flow is directed toward the heater and the other animal is drifting nearby.

Which is the most appropriate first action?

1. Switch off the heater, pour water over the jellyfish to free it gently, and move the heater to the sump
2. Peel it off the heater by hand and put it in cold water
3. Switching off the heater will chill the spotted jellyfish, so wait for it to free itself
4. Cut away the discolored area to prevent infection

AnswerA. Switch off the heater, pour water over the jellyfish to free it gently, and move the heater to the sump

ExplanationA heater inside the display tank is a classic source of injury: the current pushes jellyfish onto it and they get burned. First switch the heater off to stop the heating, then pour water from a cup or change the flow and let the animal come free naturally. Afterward keep water quality optimal and let it heal. Move the heater to the sump or an external unit and put nothing in the display tank. Peeling by hand tears the bell, and cold water adds temperature shock. Leaving it running spreads the damage. Cutting away the discolored area adds wounds and fluid loss. Switching the heater off will not drop the water from 26°C suddenly; room heating holds it for hours. If the white area melts and spreads over the next few days, consult a specialist.

IssuesKnowing zooxanthellae species need warmth, the owner made the structural error of placing the heater in the display tank, disregarding the rule that equipment inside the tank causes contact injuries and burns.

ImprovementPut the heater in the sump or use an external unit, and keep all equipment out of the display tank. Review the setup before winter and use two thermometers in different spots. Heat the whole room as well for tropical species so there is a buffer if equipment fails.

Two moon jellyfish and two spotted jellyfish have been kept together in one kreisel tank for a week. Each time they touch, the moon jellyfish bells shrink, and the spotted jellyfish oral arms have shortened too. The water is 24°C, a compromise between the two species. Both species pulse weakly and the stomach pouches color only faintly after feeding. A spare tank is in the closet.

Which is the most appropriate response?

1. Put a divider in the tank to prevent contact
2. Separate them into different tanks immediately, each with the temperature, light and flow suited to the species
3. Matching the temperature to one species will make them get along, so raise it to 26°C
4. They will get used to the injuries, so watch for a month

AnswerB. Separate them into different tanks immediately, each with the temperature, light and flow suited to the species

ExplanationDifferent jellyfish species injure each other with their stinging cells, and spotted jellyfish stings damage moon jellyfish bells. Their temperature ranges also differ: 15–25°C for moon jellyfish and 24–28°C for spotted jellyfish, so a middle value is optimal for neither. Light requirements differ as well. Separate them into different tanks as soon as possible and optimize temperature, lighting and flow for each. A divider cannot prevent contact in the current and leaves the temperature and light problems unsolved. Matching the temperature to one species does not remove the stinging problem. A month of waiting weakens both species. After separating, keep water quality optimal and let the injuries regenerate. If either begins to melt, consult a specialist.

IssuesThe owner assumed jellyfish could be mixed as long as they were all jellyfish, and housed them together without researching each species' sting strength and environmental needs. They watched injuries for a week while postponing a decision on the belief they would adapt.

ImprovementMake one tank per species the rule, and set up a dedicated tank and settings before acquiring a new species. If you want to mix species, confirm feasibility with a specialist or a proven source. Record bell and oral arm condition daily for the first week after introduction.

A weekend afternoon. A 5-year-old put a hand in the tank and poked a moon jellyfish's bell with a finger; the bell dented and the animal sank. The child is crying that the finger tingles. The jellyfish is pulsing but the bell has a finger-shaped dent. The child's fingertip is slightly red but the swelling is not spreading. There is a tap and vinegar in the kitchen.

Which is the most appropriate first action?

1. Rinse the child's finger thoroughly under tap water and push the jellyfish's bell back into shape by hand
2. Rinse the child's finger with seawater or tank water to remove tentacles, and reduce the flow to let the jellyfish rest
3. Pour vinegar on the child's finger to neutralize it and move the jellyfish to another container with a net right away
4. The jellyfish looks fine, so just take the child to the hospital

AnswerB. Rinse the child's finger with seawater or tank water to remove tentacles, and reduce the flow to let the jellyfish rest

ExplanationAttend to both the person and the jellyfish. Moon jellyfish stings are weak, but a child's skin will tingle and hurt. Rinsing with fresh water fires all the stinging cells at once, so rinse with seawater or tank water and lift off any tentacle fragments with the edge of a card. Soaking in 40–45°C water afterward eases the pain. Vinegar works for some species such as box jellyfish, but its effect on moon jellyfish is not established, so saltwater is the safe choice if in doubt. Do not reshape the jellyfish by hand; reduce the flow and let it rest and the dent will regenerate. Netting tears it. The child needs medical care if swelling spreads, breathing is difficult or hives appear over the body; mild pain only needs observation.

IssuesThe tank was placed where a child could reach in and had no lid. The family had not shared the correct sting treatment (no fresh water; rinse with saltwater).

ImprovementPlace the tank out of a child's reach and fit a lid. Teach the family "never touch the jellyfish" and "rinse stings with saltwater," and keep a small bottle of artificial seawater ready. Post the sting-treatment steps near the tank.

While siphoning leftovers from the bottom with a large pipette after feeding, a moon jellyfish drifted close and the margin of its bell was drawn into the tip, tearing off about 1 cm. The jellyfish is swimming but some stomach contents are leaking from the tear. Uncollected leftovers remain on the bottom. The other two are unharmed.

Which is the most appropriate response?

1. Push the leaked stomach contents back in with a finger
2. Stop the pipette work, gently siphon out the leaked contents and leftovers to protect water quality, and wait for the bell to regenerate
3. Blow water from the pipette in reverse to spread the bell back out
4. Do a full water change immediately to prevent infection in the torn bell

AnswerB. Stop the pipette work, gently siphon out the leaked contents and leftovers to protect water quality, and wait for the bell to regenerate

ExplanationPipette suction tears the bell by the same principle as the intake. A torn bell usually closes within days if water quality is good, so first stop the work and gently siphon out the leaked stomach contents and leftovers from a spot away from the jellyfish so they do not foul the water. Pushing contents back with a finger is impossible, destroys more tissue and gets you stung. Blowing water does not spread the bell and widens the tear. A full water change is the greatest water-quality shock and can be fatal to an injured animal. Change water in small amounts as usual, reduce the flow and let it rest. If the tear spreads from the margin toward the center or shrinkage does not stop, consult a specialist.

IssuesLeftover removal was done near the jellyfish with a large pipette, with no awareness that the suction was dangerous to the bell. The owner worked without checking where the jellyfish was.

ImprovementRemove leftovers when the jellyfish are well away, using a fine-tipped pipette or narrow hose. Pause the pump at feeding to track where the jellyfish are, and always watch the distance between the tip and the animals. Design the system so leftovers collect in the sump, reducing suction work in the display tank.

During Sunday cleaning, while scraping biofilm off the walls, the blade struck the bell of an upside-down jellyfish that drifted by, cutting about 2 cm. The jellyfish has settled on the bottom but mucus is leaking from the cut. Flakes of dislodged biofilm are floating in the tank.

Which is the most appropriate response?

1. The cut will close on its own, so leave it along with the biofilm flakes
2. Stop cleaning, siphon out the biofilm flakes and change water, and stop the flow so the upside-down jellyfish can rest
3. Lift the jellyfish and turn it over to inspect the cut
4. Add a few drops of fish medication to disinfect the wound

AnswerB. Stop cleaning, siphon out the biofilm flakes and change water, and stop the flow so the upside-down jellyfish can rest

ExplanationA scraper blade cuts a jellyfish bell easily. The cut itself regenerates in good water, but the biofilm flakes dislodged by cleaning are clumps of bacteria, and if they stick to the wound they cause infection and melting. Stop cleaning, siphon out the floating flakes, change water, and stop the flow so the upside-down jellyfish can rest on the bottom. Leaving the flakes lets the bell melt from the wound. Lifting and turning the animal widens the cut, and its mucus stings the keeper. Fish medications have no established safety for invertebrates and no disinfecting effect to speak of. If the cut turns cloudy white and spreads over the next few days, consult a specialist.

IssuesA blade was used with the jellyfish still in the tank, without checking their position. The owner did not consider that debris from cleaning could infect the wound.

ImprovementBefore wall cleaning, stop the pump, check where the jellyfish are, and always move the blade away from them. Siphon out debris and then change water after cleaning. If possible, cup the jellyfish into a separate container during cleaning.

A weekday afternoon. The breaker tripped and the pump was off for three hours. On returning home, all four moon jellyfish have sunk to the bottom, bells stuck to the floor with the margins folded. When the pump is restarted they all ride the current again, but two have bell margins rubbed white.

Which is the most appropriate response?

1. Set the flow a little stronger to spread the bells quickly
2. Set the flow to minimum, observe the abraded animals, collect leftovers to maintain water quality, and wait for the margins to recover
3. Move everyone to another tank to erase the marks from sticking to the bottom
4. Assume they will all die after sinking so long, and reset the tank

AnswerB. Set the flow to minimum, observe the abraded animals, collect leftovers to maintain water quality, and wait for the margins to recover

ExplanationWhen the pump stops, jellyfish lose the current, sink, stick to the bottom and damage their bell margins. Under 30 minutes causes little harm, but three hours produces abrasion injuries. After restarting, set the flow to minimum so the abraded bells do not hit the walls or intake, and siphon out leftovers and debris that accumulated during the stop to protect water quality. Abraded margins recover within days if water quality is good. Stronger flow widens the damaged edges. Moving everyone to another tank adds handling injuries and water shock. If they are pulsing after sinking, recovery can be fully expected, so a reset is wrong. Isolate any animal whose white areas melt and spread, and consult a specialist.

IssuesThe owner never considered the breaker might trip and had neither a pump-stop alert nor backup power. They did not know that a jellyfish tank starts sustaining damage within 30 minutes of a pump stop.

ImprovementProvide a small UPS for the pump or a pump that runs on a power bank. Use a smart plug to receive outage notifications. Put the tank on a separate circuit from other appliances and check the breaker capacity.

During a water change, a moon jellyfish drifted into the siphon hose, was sucked through, and fell into the bucket. The bucket holds the old tank water just drained. The bell is slightly folded but still pulsing. The bucket was going to be emptied down the sink. The rest of the water change is still underway.

Which is the most appropriate first action?

1. The old bucket water is dirty, so rinse the jellyfish under tap water first and then return it
2. It went through a hose so it cannot survive; dispose of it
3. Cup it out of the bucket with water, return it gently to the tank, and reduce the flow
4. Watch it in the bucket for a day before returning it to the tank

AnswerC. Cup it out of the bucket with water, return it gently to the tank, and reduce the flow

ExplanationEven with a folded bell, a jellyfish that passed through a hose has a good chance of recovery if it is pulsing. The bucket water is tank water just drained, so its salinity and temperature match the tank; cup it out with water, return it to the tank at once and reduce the flow to let it rest. Rinsing under tap water fires the stinging cells and disintegrates the tissue; it is fatal within minutes. Disposal is premature. A day in the bucket lets the temperature drop and, with no filtration, water quality deteriorates. After returning it, finish the rest of the water change carefully and watch for several days whether the fold turns cloudy and spreads. If melting begins, consult a specialist.

IssuesNo mesh was fitted on the drain hose, and draining started without checking the jellyfish's position. The owner was not aware that jellyfish cannot resist the current and are drawn toward any suction source.

ImprovementFit a mesh cover on the end of the drain hose and drain from the side away from the jellyfish. Stop the pump before a water change to locate the animals, and keep eyes on the hose end throughout. Consider cupping the jellyfish into a separate container temporarily.

While moving a spotted jellyfish in a cup for tank cleaning, the owner's hand slipped and the jellyfish fell to the floor. It lies flattened on the hardwood with dust stuck to it. It is still pulsing. There is a kitchen sink nearby, and the tank water that remained in the cup.

Which is the most appropriate first action?

1. Rinse the dust off under tap water at the sink and then return it to the tank
2. Put tank water in the cup, slide it under the jellyfish to scoop it up with water, and return it to saltwater at once
3. Wrap it in a tissue, pick it up and put it in the tank
4. It cannot survive a fall to the floor, so dispose of it

AnswerB. Put tank water in the cup, slide it under the jellyfish to scoop it up with water, and return it to saltwater at once

ExplanationA jellyfish on the floor deteriorates quickly from drying and deformation, but if it is pulsing it may recover if returned to saltwater at once. First put tank water in the cup, slide the rim under the jellyfish to scoop it up with water, and return it to the tank or a container of tank water. Tap water is fresh water: on contact, osmotic pressure disintegrates the tissue and fires the stinging cells, and it is fatal within minutes. Dust will wash off in the current once it is back in saltwater. A tissue sticks to the bell and will not come off, tearing it and stinging you. Disposal is premature. After returning it, reduce the flow, let it rest and keep water quality optimal. If the bell melts and spreads over the next few days, consult a specialist.

IssuesThe transfer cup was small and held in one hand. There was no preparation for a drop, such as a tray on the floor or using both hands. The owner did not know fresh water is fatal to jellyfish, which is why rinsing under the tap came to mind.

ImprovementMove jellyfish in a deep bowl held with both hands, over a shallow tray on the floor. Keep moves as short as possible by placing the receiving container right beside the tank. Share "no fresh water for jellyfish" with the family and keep spare artificial seawater on hand.

Woken by a noise at night, the owner finds the cat with a front paw in the lidless tank, having hooked a moon jellyfish and lifted it near the surface. When the cat is pulled away, the jellyfish drops back into the tank with its bell torn, and the cat keeps licking its paw. The jellyfish is pulsing. The cat had tried to climb onto the tank rim before, but nothing had been done about it.

Which is the most appropriate first action?

1. Net the jellyfish into a separate container and keep an eye on the cat
2. Shut the cat in another room and wipe its paw with saltwater; reduce the flow, let the jellyfish rest and maintain water quality
3. Wash the cat's mouth with tap water and straighten the jellyfish's torn bell by hand
4. The jellyfish cannot be saved, so dispose of it and take the cat to the vet

AnswerB. Shut the cat in another room and wipe its paw with saltwater; reduce the flow, let the jellyfish rest and maintain water quality

ExplanationProtect both cat and jellyfish. First shut the cat in another room away from the tank, and if tentacle fragments remain on the paw, wipe it with a cloth soaked in seawater or tank water. Licking the paw may irritate the mouth and tongue, but moon jellyfish stings are weak and serious poisoning does not normally occur. Consult a vet if drooling persists or the cat keeps pawing at its mouth. The jellyfish can regenerate even when torn as long as it is pulsing; netting tears it further, so leave it in place, reduce the flow and maintain water quality. Washing the cat's mouth with fresh water is fine, but straightening the bell by hand widens the tear and stings the keeper. Disposal is premature.

IssuesIn a home with a cat, a lidless tank was placed within the cat's reach. A moving, transparent creature is an irresistible target for a cat, and the tank was left unprotected at night.

ImprovementFit a gap-free lid and place the tank at a height the cat cannot climb to or in a cabinet with doors. Close the room at night. Know the signs to watch if the cat licks a jellyfish (drooling, mouth discomfort) and keep the vet's number handy.

Checking the sump, the owner finds that the mesh over the display tank's overflow has come off and two moon jellyfish have dropped into the sump, wedged between the filter media. The sump contains an air stone, and one animal is enveloped in bubbles and pressed against the surface. Both are pulsing.

Which is the most appropriate first action?

1. Stop the pump and aeration, cup them out with water back into the display tank, and refit the mesh
2. Pinch them out from between the filter media with your fingers
3. Leave the pump running and wait for the current to carry them back to the display tank
4. Drain the sump completely and pick the jellyfish up off the bottom

AnswerA. Stop the pump and aeration, cup them out with water back into the display tank, and refit the mesh

ExplanationWashing out through the overflow happens because jellyfish cannot resist the current. First stop the pump and aeration to remove the suction and bubbles. The animal enveloped in bubbles is prone to bell holes, so gently cup it out with water and return it to the display tank. For the wedged animal, gently shift the filter media to open a gap and cup it out the same way. Pinching with fingers tears the bell and stings the keeper. With the pump running they stay pressed against the media and the damage spreads; they will never return to the display tank on their own. Draining all the water exposes them to air and deforms them. Afterward, secure the mesh, review the flow rate, and watch for bell damage over the next few days.

IssuesThe overflow mesh was loosely fitted, and the setup gave no sign when it came off. The air stone in the sump was positioned so that washed-out animals suffered secondary damage.

ImprovementSecure the overflow mesh with cable ties or a purpose-made cover and check for shifting in the daily inspection. Position the sump air stone where washed-out animals are unlikely to reach it. Make it a habit to look into the sump daily to check for jellyfish.

Back from a week-long business trip, the owner finds the water level 3 cm low and adds 2 L of filtered tap water in one go through a hose into the display tank. Fifteen minutes later all three spotted jellyfish have contracted their bells; two have sunk to the bottom and are pulsing weakly. The hydrometer reads 1.018. The spotted jellyfish look paler and their oral arms are retracted. Spare artificial seawater is on hand.

Which is the most appropriate response?

1. Add more fresh water to lower the temperature and calm them
2. Add salt mix directly to the tank to restore salinity in one go
3. Add saltwater at matched salinity in small amounts over several hours, gradually bringing it back above 1.021
4. Fresh water mixes quickly, so wait a day and they will recover on their own

AnswerC. Add saltwater at matched salinity in small amounts over several hours, gradually bringing it back above 1.021

ExplanationCorrecting evaporation-raised salinity with fresh water is right in itself, but dumping a large volume into a small tank at once makes salinity plunge, and osmotic shock contracts and sinks the bells. The remedy is to add saltwater mixed to around 1.024 in small amounts over several hours, gently bringing salinity back to 1.021–1.024. Adding salt directly creates pockets of highly concentrated brine that damage any animal they touch. More fresh water deepens the shock. Waiting a day is too slow for animals already sunk in shock. Afterward reduce the flow, remove leftovers and let them rest. If pulsing has not returned after half a day and melting begins, consult a specialist.

IssuesNo top-up arrangement was made before a long absence, and on returning the owner rushed and added a large volume of fresh water at once. They did not understand the basic rule of topping up a little at a time or how sudden salinity changes affect jellyfish.

ImprovementTop up in small amounts daily, using an auto top-off unit or a drip container. For long absences, ask family or a friend to feed and top up, and leave written instructions. Always use the hydrometer before leaving and after returning, and record top-up volumes.

A winter morning. The moment the owner puts a hand in the sump to clean out leftovers, their fingertips tingle with a shock. The glass tube of the heater has cracked and the power cord is submerged. The three spotted jellyfish are swimming in the tank, but the water has dropped to 23°C.

Which is the most appropriate first action?

1. Quickly lift the heater out by hand and replace it
2. Put on rubber gloves, drain all the tank water and remove the heater
3. Take your hand out, cut the power at the outlet or breaker, then remove and replace the heater with dry hands
4. Move the jellyfish to a separate container first, then check the heater

AnswerC. Take your hand out, cut the power at the outlet or breaker, then remove and replace the heater with dry hands

ExplanationElectrical leakage into water is life-threatening to the keeper. First take your hand out of the water, and without touching the outlet with wet hands, unplug it or trip the breaker with dry hands to cut the power completely. Then remove the cracked heater with dry hands, replace it with a new one and return it to the sump. Lifting the heater with the power on carries the highest risk of electrocution. Rubber gloves are no guarantee of insulation, and a full water change is a major shock to the jellyfish. Putting your hand in the water to move the jellyfish first is also dangerous. Once the power is off, the jellyfish are not urgent at 23°C; warm the room and bring them back to 25–28°C with the new heater. See a doctor if numbness persists or palpitations occur.

IssuesThe heater had not been inspected for cracks. The tank was on a circuit without a ground-fault interrupter, and there was no habit of cutting the power before working in the tank. The owner was not prepared to put human safety ahead of the jellyfish.

ImprovementUse a power strip with a ground-fault interrupter on the aquarium circuit and always switch off the heater and pump before putting a hand in the water. Inspect the heater's glass tube and cord monthly and switch to a shielded or titanium heater. Keep a spare heater on hand.

For a house move, three moon jellyfish were bagged the way fish are, with plenty of air at the top, and driven for two hours. On arrival, the sloshing had frothed the air under the bells: two bells have holes and one is inverted. The water had reached 24°C in the car.

What is the most appropriate action to take now?

1. Float the bag in the new tank to equalize temperature, cup them across with water, draw off the bubbles and let them rest
2. Quickly pour them from the bag into the tank and blow the bubbles off with strong flow
3. The animals with holes cannot be saved, so move only the inverted one to the tank
4. Discard the bag water, rinse the bells under tap water and put them in the tank

AnswerA. Float the bag in the new tank to equalize temperature, cup them across with water, draw off the bubbles and let them rest

ExplanationThe rule for transporting jellyfish is no air: fill the bag completely with water and seal it, because air froths with motion and damages the bells. Even with existing damage, recovery is possible as long as they are pulsing. Float the bag in the tank for at least 30 minutes to equalize temperature, add tank water gradually to bring salinity closer, and transfer with water in a cup. Draw off any bubbles still on the bells with a pipette, set the flow to minimum and let them rest. Pouring them in and strong flow spread the damage. Holes close within days in good water, so giving up is premature. Tap water is fresh water and fatal. Feed lightly for a few days after the move, and isolate any animal that begins to melt.

IssuesThe owner applied fish transport methods to jellyfish, unaware that bubbles tear bells. There was no temperature control in the car and the water warmed during the two-hour trip.

ImprovementTransport jellyfish in a bag or bottle filled with tank water and sealed with no air, in an insulated bag to hold the temperature. Wrap in a towel to limit motion and keep the trip as short as possible. Set up the tank at the new home beforehand at the same salinity and temperature.

After an ich outbreak in a separate marine fish tank, the owner added a copper-based fish medication at the recommended dose to the jellyfish tank as a precaution. Two hours later, the three upside-down jellyfish have lifted off the bottom with contracted bells, and their oral arms are turning white and breaking down as if dissolving. Pulsing is still faintly present.

Which is the most appropriate first action?

1. Wait for the medication to take effect and check again tomorrow
2. Add activated carbon to the sump to neutralize the medication and leave the jellyfish where they are
3. Halve the dose by draining half the tank water and topping up with fresh water
4. Cup them immediately into a separate container of stable, medication-free saltwater, and do a full water change on the main tank to remove the drug

AnswerD. Cup them immediately into a separate container of stable, medication-free saltwater, and do a full water change on the main tank to remove the drug

ExplanationCopper is lethal to invertebrates including jellyfish even in trace amounts, and dissolving oral arms mean poisoning is already advanced. The top priority is to cup them at once into a separate container of stable, medication-free saltwater at matched salinity and temperature. Do a full water change on the main tank, remove residual copper with activated carbon, and wash the tank and filter media thoroughly before returning them. Copper lingers in silicone and filter media, so keep running carbon for a while. Waiting until tomorrow means total loss. Carbon alone removes it slowly and the jellyfish stay exposed. Adding fresh water adds a second shock from the salinity plunge. Animals that keep dissolving after the move are hard to save, but if pulsing continues, maintain water quality and watch.

IssuesThe owner did not know that fish medications, especially copper, are lethal to invertebrates and dosed a healthy jellyfish tank as a precaution. There was no habit of checking which animals a medication is intended for.

ImprovementMake it a rule to add no medications or additives of any kind to the jellyfish tank. Keep fish-tank and jellyfish-tank equipment completely separate and never touch the jellyfish tank with hands that have handled medication. Get in the habit of checking ingredient labels for copper and malachite green.

A summer night. Bitten by mosquitoes in the room with the tank, the owner sprayed an aerosol insecticide for a few seconds near the lidless tank. Next morning the four moon jellyfish are pulsing irregularly, two have folded their bells and sunk, and a thin oily film floats on the water. The spray can is still next to the tank and the room has not been ventilated. The film covers the whole surface.

Which is the most appropriate response?

1. Blot the film off with paper towels, do a 50% water change with saltwater matched for salinity and temperature, add activated carbon and ventilate
2. The film is harmless; deal with it at the regular water change in a few days if it bothers you
3. Spray deodorizer in the room to get rid of the insecticide smell
4. Move the jellyfish temporarily into a container of tap water to rinse off the insecticide

AnswerA. Blot the film off with paper towels, do a 50% water change with saltwater matched for salinity and temperature, add activated carbon and ventilate

ExplanationInsecticides such as pyrethroids settle on the surface and dissolve into the water, and they are highly toxic to invertebrates like jellyfish. The oily film is the evidence. First blot the surface film off with paper towels, change about 50% of the water with saltwater matched for salinity and temperature, add activated carbon to the sump to adsorb the residue, and ventilate the room. Continue water changes the next day. Leaving it for days risks losing them all. Deodorizer only adds more chemicals and does not remove the toxin from the water. Tap water is fresh water and fatal. Isolate any animal whose pulsing does not return and that begins to melt after the water change, and consult a specialist.

IssuesThe owner did not know that insecticide enters the tank from the surface and is toxic to invertebrates. The tank had no lid and no thought was given to covering it while spraying.

ImprovementNever use aerosol insecticides, air fresheners or deodorizing sprays in the room with the tank. Control mosquitoes with nets and physical measures. Fit a lid, and if spraying is unavoidable, cover the tank with a cloth, spray in another room, and ventilate.

A winter night. Right after applying hand cream for chapped skin, the owner put a bare hand in the tank to reposition the pipette and fed brine shrimp. Next morning an oily film covers the surface, two spotted jellyfish have white spots on their bells and are pulsing weakly. Gloves had been bought but never used. There is no activated carbon in the sump.

Which is the most appropriate response?

1. The white spots are disease, so give a medicated bath with a fish remedy
2. Blot off the film, do a 30% water change, add activated carbon, and use gloves from now on
3. The film will evaporate, so leave it and just reduce feeding
4. Suck the spots off the bells with a pipette to clean them

AnswerB. Blot off the film, do a 30% water change, add activated carbon, and use gloves from now on

ExplanationOils and surfactants in hand cream, soap and sunscreen form a surface film that blocks gas exchange and directly damage the jellyfish's body surface; the white spots are that irritation. Blot the film off with paper towels, change 30% of the water with saltwater matched for salinity and temperature, and adsorb the residue with activated carbon. Work with disposable gloves from now on. Fish medications are dangerous to invertebrates and the cause is not something medication cures. The film does not evaporate, and the spots spread if left. Sucking at the spots punches holes in the bell. Isolate any animal whose spots melt and spread over the next few days and consult a specialist.

IssuesThe owner worked bare-handed without considering how concentrated chemicals from the hands become in a small tank. Working with chapped skin also posed an infection risk to the keeper.

ImprovementAlways wear disposable gloves for tank work and rinse hands in plain water, without soap, beforehand. Apply hand cream or sunscreen after the work. Keep gloves and paper towels for film removal beside the tank.

In summer the owner netted plankton at the seaside and added it to the moon jellyfish tank as "natural food." Three days later, tiny jellyfish of another species and creatures with tentacles are swimming in the tank, the moon jellyfish have red spots and chips on their bells and are starting to shrink, and the water is cloudy. The small jellyfish can be seen extending tentacles that touch the moon jellyfish's bells. Spare artificial seawater is available.

Which is the most appropriate response?

1. It is natural food, so there is no problem; keep feeding it
2. Remove only the foreign creatures with a net and leave the water as is
3. Cup the moon jellyfish into a separate container of stable saltwater, and remove the introduced organisms from the main tank with water changes and cleaning
4. Raise the water temperature to 35°C to kill the introduced organisms

AnswerC. Cup the moon jellyfish into a separate container of stable saltwater, and remove the introduced organisms from the main tank with water changes and cleaning

ExplanationNatural seawater and live food bring other cnidarians, parasites, pathogens and plankton toxins into the tank. The red spots and chips on the bells are most likely sting marks from the introduced cnidarians or parasitism. Cup the moon jellyfish into a separate container of stable artificial seawater at matched salinity and temperature, and clear the introduced organisms from the main tank with water changes and cleaning of the walls and sump. Continuing to feed it spreads the damage. Netting out the creatures leaves microscopic larvae and eggs behind and does nothing for the fouled water. A temperature of 35°C is lethal to moon jellyfish, which defeats the purpose. If the moved animals keep shrinking and begin to melt, consult a specialist.

IssuesThe owner believed natural live food was safe and nutritious, unaware of the danger of introducing unknown organisms and pathogens. They departed from the jellyfish-keeping basic of newly hatched brine shrimp.

ImprovementLimit food to newly hatched brine shrimp or commercial jellyfish food. Never put natural seawater, live food or seaweed in the tank. Try any new food in small amounts in a separate container, and check expert information before bringing it to the tank.

In a tank with fine sand for upside-down jellyfish, the flow was too strong and stirred up the sand; the next day several sand grains can be seen through the body inside one animal's stomach. Its oral arms move weakly and the stomach pouches do not color after feeding. The other animals are normal.

Which is the most appropriate response?

1. Pick the sand grains out of the stomach one by one with tweezers
2. Reduce the flow so the sand stays settled, maintain water quality while waiting for natural expulsion, and assist feeding with a pipette
3. Remove all the sand and convert to a bare tank with a same-day reset
4. Aim strong flow directly at the bell to flush out the stomach

AnswerB. Reduce the flow so the sand stays settled, maintain water quality while waiting for natural expulsion, and assist feeding with a pipette

ExplanationWhen jellyfish take foreign matter into the stomach, most of it is expelled naturally through the mouth. Trying to pull it out with tweezers tears the soft bell and stomach, and the upside-down jellyfish's mucus stings the keeper. Reduce the flow that caused the sand to stir up, keep water quality optimal, pause the pump at feeding and release food near the oral arms with a pipette to confirm it can eat while waiting for expulsion. Removing all the sand for a same-day reset is a major water-quality shock; upside-down jellyfish do fine on fine sand or a bare tank, so there is no need to rush. Strong flow aimed at the bell damages it. If the stomach pouches still do not color and shrinkage continues after a week, consult a specialist.

IssuesSand was added to the upside-down jellyfish tank, yet the flow was set strong enough to stir it up. Daily checks of stomach-pouch color would have caught the problem sooner.

ImprovementSet the flow in an upside-down jellyfish tank to the minimum at which sand does not move, and use a thin layer of fine sand or a bare tank. Check stomach-pouch color and foreign matter at every feeding, and always watch the sand whenever the flow setting changes.

On an August day, in a closed room, the water climbed to 31°C. On returning home, the three moon jellyfish have contracted bells, drift near the surface and pulse irregularly. One bell margin is starting to melt. There is air conditioning, but it was off while out. A cooling fan and ice packs are in the closet. Feeding was in the morning and leftovers remain on the bottom.

Which is the most appropriate first action?

1. Drop ice straight into the tank to chill it fast
2. Replace half the water at once with saltwater chilled in the refrigerator
3. Turn on the air conditioning and cooling fan, hold ice packs against the outside of the tank to lower it 1–2°C per hour, and remove the leftovers
4. Let them acclimate to the heat and wait for the natural drop at night

AnswerC. Turn on the air conditioning and cooling fan, hold ice packs against the outside of the tank to lower it 1–2°C per hour, and remove the leftovers

ExplanationThe moon jellyfish's range is 15–25°C, and 31°C is the danger zone where bells begin to melt. But rapid cooling causes temperature shock that inverts the bells further, so cool the room and the surface with the air conditioning and fan, hold ice packs against the outside of the tank, and bring it down to 25°C or below at 1–2°C per hour. Leftovers rot fast in heat, so siphon them out and test ammonia. Ice dropped in is fatal from pockets of fresh water and sudden chilling. A half-volume change with chilled saltwater is also too abrupt. Waiting until night risks the melting progressing and losing them all. Once the temperature is restored, isolate the animal with the melting margin, keep water quality optimal and observe.

IssuesThe owner switched off the air conditioning during a summer day, underestimating how quickly a small tank follows room temperature. No cooling that works while away, such as a fan or chiller, had been set up.

ImprovementIn summer run the air conditioning continuously or automate a chiller and cooling fan on a thermostat. Use a logging thermometer or one with alerts so the temperature can be checked remotely. Keep the tank in a room without direct sunlight.

A January night. Heavy snow has caused a power outage; heating, heater and pump are all off and there is no estimate for restoration. The tank with three spotted jellyfish has dropped from 26°C to 22°C in two hours and the jellyfish are starting to sink. Available: hand warmers, blankets, a styrofoam box and a power bank.

Which is the most appropriate response?

1. Enclose the tank in the styrofoam box and blankets, stick hand warmers on the inside walls of the box for gentle warmth, and run the pump from the power bank
2. Drop hand warmers directly into the tank water to raise the temperature
3. Boil water and pour it into the tank to get back to 26°C right away
4. Put the jellyfish in a cup and warm them against your body

AnswerA. Enclose the tank in the styrofoam box and blankets, stick hand warmers on the inside walls of the box for gentle warmth, and run the pump from the power bank

ExplanationSpotted jellyfish are tropical and begin to weaken below 20°C. The goal during an outage is to halt the rapid drop and hold the temperature gently until power returns. Put the tank in the styrofoam box, cover with blankets, and stick hand warmers on the inside walls of the box, not in contact with the water, for indirect warmth. Keep the water moving from the sump with a small pump or air pump that runs on the power bank, so they do not sink and abrade on the bottom. Hand warmers in the water pollute it and heat it unevenly. Hot water poured in causes shock from sudden temperature and salinity changes. Warming them against your body deforms the bells and stings the keeper. Keep logging the temperature and, after power returns, raise it 1–2°C per hour.

IssuesNo warming measures or backup power had been prepared for a winter outage, and there was no outage plan despite keeping a tropical species. The situation invited the mistake of trying to warm them too fast.

ImprovementAssemble a styrofoam box, blankets, hand warmers and a power-bank air pump into an "outage kit" near the tank. Post an outage procedure and rehearse it before winter. Consider a UPS and an outage-alert app.

A strong earthquake (JMA intensity 5+) strikes late at night. A third of the tank water has spilled, the pump has stopped, and an evacuation order has been issued. The three moon jellyfish have sunk in the remaining water but are pulsing. Only a small bag can be taken to the shelter, and returning home is expected to take 1–2 days.

Which is the most appropriate response?

1. Give up on the jellyfish and evacuate thinking only of your own safety
2. Carry the whole tank to the shelter
3. Cup them into a sealable wide-mouth container of tank water, seal with no air, carry in an insulated bag, and keep them still at the shelter
4. Top the tank up with tap water, restart the pump, then evacuate

AnswerC. Cup them into a sealable wide-mouth container of tank water, seal with no air, carry in an insulated bag, and keep them still at the shelter

ExplanationHuman safety comes first, but with a few minutes to spare the jellyfish can come too. The basics of transport are a sealed container filled with tank water, no air, and protection from motion and temperature change. Cup them with water into a plastic bottle or wide-mouth food container, wrap in a towel, put in an insulated bag, and keep them in a dark, quiet place at the shelter. They tolerate 1–2 days without feeding. The whole tank is heavy and may shatter in an aftershock. Tap water sends salinity plunging and is fatal on the spot, and the pump will not run without power. Before giving up, a few minutes spent moving them to a container gives a good chance of saving them. On return, set the tank up again with new saltwater and match temperature and salinity before putting them back.

IssuesThe owner had not anticipated an earthquake spilling the water and stopping the pump, and had prepared no carry container, spare saltwater or insulated bag. No anti-tip measures or seismic mats had been installed.

ImprovementPut a seismic mat under the tank and fit a lid to reduce spills. Keep a sealable wide-mouth container, spare artificial seawater, an insulated bag and a cup together as a "grab-and-go kit" near the tank. Share the shelter care procedure with the family.

The owner left for a 10-day trip without arranging top-ups and with the air conditioning off. On return the water level is 5 cm low and the hydrometer reads 1.030. The three moon jellyfish have contracted bells that look stiff, and pulsing is weak. The water is 27°C and a trace of ammonia is detected. Before the trip it was stable at 1.023 and 24°C. Filtered fresh water and spare artificial seawater are on hand.

Which is the most appropriate response?

1. Pour in 5 cm worth of fresh water at once to restore the level and salinity
2. Drip fresh water in slowly over several hours to bring salinity down gradually to 1.024, and remove the ammonia with water changes at the same time
3. High salinity alone is no problem, so resume normal feeding
4. They cannot tolerate high salinity, so replace all the water with new saltwater

AnswerB. Drip fresh water in slowly over several hours to bring salinity down gradually to 1.024, and remove the ammonia with water changes at the same time

ExplanationWhen evaporation pushes salinity up to 1.030, osmosis draws water out of the jellyfish and the bells contract and stiffen. Correct it without abrupt change: drip filtered fresh water in over several hours, bringing salinity down gently to 1.024. In parallel, change water in small amounts with saltwater at matched salinity to remove the ammonia concentrated by leftovers and evaporation. A large dose of fresh water at once causes the opposite, low-salinity shock, and inverts the bells. Ignoring the salinity lets the shrinkage progress. A full water change is the greatest possible shock and fatal to weakened animals. Afterward bring the temperature gently down to 25°C or below and resume light feeding the next day. Isolate any animal whose pulsing does not return and consult a specialist.

IssuesNo top-up arrangement or temperature control was made for a 10-day absence. The owner underestimated how fast salinity climbs from evaporation in a small jellyfish tank.

ImprovementFor absences over three days, install an auto top-off unit or a drip top-up container. Ask family or a friend to top up and remove leftovers, leaving written instructions that include how to use the hydrometer. Keep the air conditioning on low while away in summer.

The LED light on a spotted jellyfish tank failed and stayed off for a week before anyone noticed. The jellyfish's brown color has faded and they are starting to shrink; feeding was only every other day. The water is 26°C, salinity 1.023, and water quality is fine. The owner is considering moving the tank to a window with strong direct sunlight as a substitute light.

Which is the most appropriate response?

1. Move the tank into direct sunlight at the window to give the zooxanthellae light
2. Lighting is only for display and not needed; returning to daily feeding is enough
3. Press an ordinary incandescent bulb right on top of the tank for strong light
4. Replace the full-spectrum aquarium LED, return to 8–10 hours a day, and increase feeding to 1–2 times daily

AnswerD. Replace the full-spectrum aquarium LED, return to 8–10 hours a day, and increase feeding to 1–2 times daily

ExplanationSpotted jellyfish depend heavily on photosynthesis by their zooxanthellae; a week without light depletes the zooxanthellae and bleaching and shrinkage begin. Replace the full-spectrum aquarium LED immediately and return to 8–10 hours a day on a timer. At the same time increase feeding to 1–2 times daily to supply nutrition until the zooxanthellae recover. Direct sunlight sends the temperature soaring and triggers algae blooms, which is fatal in a small tank. The idea that lighting is unnecessary is wrong; feeding alone does not stop bleaching. An incandescent bulb heats the water and its wavelengths are unsuitable for photosynthesis. If color does not return and shrinkage continues after two weeks, consult a specialist.

IssuesThe owner did not understand that lighting is a lifeline for zooxanthellae species, and the failure went unnoticed for a week through lack of observation. There was no spare light and feeding was insufficient.

ImprovementAutomate lighting on a timer and add a lighting check to the daily inspection. Keep a spare LED and replace a failed one the same day. Fix the feeding plan on the premise that zooxanthellae species need daily feeding in addition to light.

During a water change with bare hands, a spotted jellyfish's tentacles brushed the owner's arm, causing a tingling pain and red streaks. Fine tentacle fragments cling to the arm. A tap and vinegar are right there, and the family is saying "rinse with fresh water and put vinegar on it." The tingling is spreading, the pain is bearable, and breathing is normal.

Which is the most appropriate treatment?

1. Scrub the arm under tap water and pour on plenty of vinegar
2. Rinse with seawater or tank water, lift off the tentacle fragments with the edge of a card, and soak in 40–45°C water
3. Rub the tentacles off with a towel and apply ice
4. The tentacles will fall off on their own, so carry on with the water change

AnswerB. Rinse with seawater or tank water, lift off the tentacle fragments with the edge of a card, and soak in 40–45°C water

ExplanationThe basic principle of treating a sting is to stop any more stinging cells from firing. Fresh water fires them all at once by osmosis and makes it worse. Rinse with seawater or tank water and lift off attached tentacle fragments with tweezers or the edge of a card. Then soak in 40–45°C water for about 20 minutes to inactivate the venom and ease the pain. Vinegar is effective for some species such as box jellyfish, but its effect on the three kept species is not established, and it makes Portuguese man o' war stings worse. If in doubt, saltwater is safe. Rubbing with a towel drives stinging cells into the skin, and ice relieves pain temporarily but leaves the venom. Carrying on with the work adds more stings. Go to the emergency room if swelling spreads, breathing becomes difficult or hives appear over the body.

IssuesThe owner put bare hands in the tank and had not shared correct sting treatment with the family. They did not know that the beach lore of "fresh water and vinegar" does not apply to the kept species.

ImprovementAlways wear gloves for tank work. Keep a small bottle of artificial seawater, tweezers and a card beside the tank and post the treatment steps on the wall. Teach the family "never rub with fresh water" and "rinse with saltwater," and share the signs of a severe reaction and the emergency number.

The day after cutting a finger while cooking, the owner cleaned the jellyfish tank bare-handed with just an adhesive bandage on. That night the finger turned red, swollen and hot; by next morning the redness has spread to the back of the hand, with a 38°C fever and chills. The jellyfish are fine. The cut was deep and the skin under the bandage was damp. No underlying illness, but the swelling has visibly spread within hours.

Which is the most appropriate response?

1. Assume a jellyfish sting, apply vinegar and watch
2. Suspect a wound infection from bacteria in the seawater; see a doctor today and mention the aquarium work
3. Disinfect with an over-the-counter antiseptic and wait a few days for the swelling to go down
4. The jellyfish tank is the cause, so dispose of all the jellyfish

AnswerB. Suspect a wound infection from bacteria in the seawater; see a doctor today and mention the aquarium work

ExplanationSeawater contains bacteria such as Vibrio species, which enter through broken skin and cause rapidly spreading wound infections. Redness spreading within hours with fever and chills needs urgent treatment, and it is especially likely to become severe in people with liver disease or diabetes. See a doctor today and explain the saltwater aquarium work and how the injury happened, so the right treatment can be given. Vinegar is a sting remedy, useless for infection, and these are not sting symptoms anyway. Antiseptic alone with days of waiting misses the progression. The jellyfish are not the source; bacteria normally present in the tank water entered through the wound, so disposing of them is pointless. After recovery, use gloves without exception.

IssuesThe owner touched seawater with a wounded hand, not knowing an adhesive bandage cannot keep bacteria out. There was no awareness that saltwater aquarium work carries an infection risk for people.

ImprovementWhen you have a hand wound, skip tank work or use long disposable gloves. Wash hands with soap afterward. Decide in advance to see a doctor the same day if redness spreads rapidly or fever develops. Family members with underlying conditions should avoid tank work.

Six months into keeping jellyfish, always working bare-handed. A month ago a reddish-purple lump appeared on the back of the hand; it is painless but growing, and a new lump has appeared on the wrist. Over-the-counter ointment has made no difference. The jellyfish are healthy. The lumps are multiplying in a line from the back of the hand to the wrist along the inside of the arm. The hands often get small cuts.

Which is the most appropriate response?

1. They are jellyfish sting marks and will fade if left alone
2. Add a jellyfish-safe antibacterial to the tank to reduce the causative bacteria
3. See a dermatologist, explain that you handle a saltwater aquarium bare-handed, and get tested
4. Lance the lumps with a needle and squeeze out the contents

AnswerC. See a dermatologist, explain that you handle a saltwater aquarium bare-handed, and get tested

ExplanationNon-healing reddish-purple lumps that spread in sequence from the hand up the arm suggest aquarium granuloma, caused by mycobacteria in seawater entering through small skin wounds. The aquarium history is essential for diagnosis, and ordinary antibiotics are often ineffective, so see a dermatologist, explain that you handle a saltwater aquarium bare-handed, and get tested. Left alone it spreads over months. Medication in the tank only kills the jellyfish and does nothing for the lesions on human skin. Lancing with a needle spreads the infection and leaves scars. Treatment can take months, but the earlier it starts the milder it is. Use gloves without exception for all future work.

IssuesThe owner handled seawater bare-handed for six months, unaware of infections that saltwater aquariums can pass to people. They self-diagnosed the lumps as sting marks and delayed seeing a doctor for a month.

ImprovementMake gloves the rule for tank work and wash hands afterward. For any non-healing lump or ulcer on the skin, do not self-diagnose; see a dermatologist and report the aquarium. Share the same rules with the family and never run out of work gloves.

The owner hatches brine shrimp daily and measures the dry eggs in the kitchen. Lately every measuring session brings coughing and sneezing, and some nights breathing is difficult. The owner's wife has started showing the same symptoms. The hatchery is in a poorly ventilated room, and a white layer of egg dust has settled near the tank. There is no plan to stop feeding, and the cause is unclear.

Which is the most appropriate response?

1. Suspect sensitization to dry-egg dust; measure with a mask and ventilation or in a sealed container, and see a doctor if symptoms persist
2. Jellyfish venom is drifting in the air, so putting a lid on the tank will solve it
3. The cough is a cold; use over-the-counter medicine and keep feeding as before
4. Symptoms mean the food must change, so switch to plankton collected from the sea

AnswerA. Suspect sensitization to dry-egg dust; measure with a mask and ventilation or in a sealed container, and see a doctor if symptoms persist

ExplanationThe shells of dry brine shrimp eggs become fine dust that, when inhaled, can cause allergic coughing and asthma-like symptoms. When the daily handler and a household member both have symptoms, first reduce exposure to the dust. Measure in a well-ventilated place wearing a mask, handle the eggs in a sealed container, and move the hatchery away from the bedroom. Consider switching to decapsulated eggs or commercial jellyfish food. If nighttime breathlessness persists, see a respiratory specialist and describe the setup. Sting venom does not drift in the air, so a lid solves nothing. Treating it as a cold and continuing exposure makes the symptoms chronic. Sea plankton risks introducing pathogens to the tank.

IssuesThe owner did not know that the dry eggs handled daily affect the airways as dust, and measured them uncovered in a poorly ventilated room. The cause went unrecognized until a family member had symptoms too.

ImprovementMeasure dry eggs with a mask under ventilation, using a sealed container and spoon so no dust rises. Keep the hatchery in a ventilated space away from the bedroom and living room. Try decapsulated eggs or commercial food, and keep a record of symptoms including the family's.

6 a.m. All four moon jellyfish have stopped pulsing and are drifting at the surface and on the bottom. They were normal last night. The water is clear, but the filter sponge was replaced with a new one yesterday. Water is 20°C, salinity 1.022. Test kits show clearly detectable ammonia and nitrite.

Which is the most appropriate first action?

1. Put an air stone in the tank to supply oxygen
2. Judge all non-pulsing animals dead and dispose of them
3. Cup them into a separate container of new saltwater at matched salinity and temperature, and check for bell contraction with a gentle flow
4. Offer food and see whether they respond

AnswerC. Cup them into a separate container of new saltwater at matched salinity and temperature, and check for bell contraction with a gentle flow

ExplanationReplacing the filter sponge wiped out the bacteria, ammonia and nitrite spiked, and the jellyfish were poisoned. Jellyfish have no heart or lungs, so "resuscitation" consists entirely of moving them from toxic water to safe water. Cup them into a separate container of new saltwater at matched salinity and temperature and judge life by whether the bell contracts under a very gentle flow. If it contracts, pulsing usually returns within hours. An air stone in the tank punches holes in the bells and does not remove ammonia. Declaring death from stopped pulsing alone is premature; there is room for recovery until melting begins. They will not eat while poisoned and food fouls the water further. Keep changing water in the main tank and do not return them until ammonia is zero.

IssuesThe filter sponge was replaced all at once with a new one, destroying the filter bacteria. The owner did not know that in a small jellyfish tank ammonia can reach lethal levels overnight, and did no water test after the replacement.

ImprovementReplace filter media half at a time on staggered dates and test ammonia daily for three days afterward. Keep spare saltwater always ready and an emergency isolation container ready for immediate use. Learn the rule "pulsing stopped = move to safe water."

Evening. One moon jellyfish lies on the bottom with its bell spread open, motionless. The other two are circling normally. Water quality, salinity and temperature are all correct. The sunken animal shows no cloudiness or melting and its shape is intact. The owner wants to remove it if dead but cannot tell.

Which is the most appropriate way to check whether it is alive?

1. Pinch the bell with tweezers, lift it and see if it moves
2. Direct a very gentle flow at the bell with a pipette and watch for contraction and the resumption of pulsing
3. Take it out of the tank, place it on your palm and watch for a response
4. Drop food onto the bell and see if it eats

AnswerB. Direct a very gentle flow at the bell with a pipette and watch for contraction and the resumption of pulsing

ExplanationWhether a jellyfish is alive is judged by the bell's contraction response. A healthy moon jellyfish pulses regularly about 30–60 times a minute, but it can also pause pulsing temporarily and sink. Direct a very gentle flow at the bell with a pipette; if the bell contracts or pulsing resumes, it is alive. If there is no response and the bell is melting and losing its shape, judge it dead and remove it to protect the water for the others. Pinching with tweezers tears the bell even if it is alive, and stings the keeper. Taking it out into the air deforms the bell and damages a living animal. A response to food is hard to read and becomes leftovers. If alive, reduce the flow, let it rest and observe until the next day.

IssuesThe owner did not know a safe way to check for life and nearly used damaging methods such as pinching or removing it. They did not know the normal pulse rate or that temporary pauses in pulsing occur.

ImprovementObserve and record the normal pulse rate and posture so changes are noticeable. Learn "check for contraction with a gentle flow" as the life check and keep a pipette beside the tank. Also confirm the criteria for death (melting, loss of shape).

Staff at a public aquarium who know invertebrates have agreed to look at a spotted jellyfish whose bell is half melted. It is an hour's drive. On hand: zip bags, a wide-mouth bottle, tank water, an insulated bag and hand warmers. It is December and the outdoor temperature is 8°C.

Which is the most appropriate transport method?

1. Half-fill a bag with tank water and inflate it with plenty of air
2. Fill the bottle with tap water to keep it light, add the jellyfish and go
3. Fill the wide-mouth bottle with tank water, seal with no air, and carry it in the insulated bag with hand warmers on the outside, avoiding vibration and light
4. Load the whole tank into the car

AnswerC. Fill the wide-mouth bottle with tank water, seal with no air, and carry it in the insulated bag with hand warmers on the outside, avoiding vibration and light

ExplanationThe most important rule in transporting jellyfish is to leave no air in the container. Air froths with motion and punches holes in the bell. Fill the wide-mouth bottle with tank water, cup the jellyfish in with water, and seal with no air left. As a tropical species it chills quickly in December air, so place hand warmers inside the insulated bag wrapped in a towel so they do not touch the container, and carry it away from vibration and light. Plenty of air is the fish method and is counterproductive for jellyfish. Tap water is fresh water and fatal. Carrying the whole tank sloshes the water, slams the bell against the walls, and is heavy and dangerous. Bring the records of temperature, salinity, ammonia and feeding, plus photos of the tank.

IssuesThe transport supplies were ready, but the owner nearly chose the air-filled method used for fish. There was no concrete plan for the winter cold and the owner had not learned the jellyfish-specific transport method.

ImprovementWrite down and keep the jellyfish transport procedure (no air, sealed, insulated, no vibration). Keep the husbandry logbook up to date so it can be presented at once. Look up in advance the contact details of aquariums or vets that treat invertebrates.

A moon jellyfish whose bell was badly torn in an intake accident. After it was freed and returned, stomach contents keep streaming from the tear and the surrounding water is turning cloudy white. The other two are in the same tank. It is pulsing. Spare saltwater and a small container are available. The tear runs from the bell margin almost to the center; the oral arms are intact. The cloudiness is gradually spreading through the tank.

Which is the most appropriate response?

1. Press the tear closed with a finger
2. Cup the torn animal into a separate container of clean saltwater to isolate it, and siphon out the cloudiness and change water in the main tank
3. It is like bleeding, so add a hemostatic agent to the tank
4. Leave the torn animal where it is and move the other two to a separate container

AnswerB. Cup the torn animal into a separate container of clean saltwater to isolate it, and siphon out the cloudiness and change water in the main tank

ExplanationJellyfish have no blood; the equivalent of "stopping bleeding" is keeping the leaking stomach contents from fouling the water and letting the injured animal rest in clean water. Cup the torn animal into a separate container of clean saltwater at matched salinity and temperature, with no flow, and let it rest. Siphon out the cloudiness and change water in the main tank to protect the other two. Pressing with a finger tears the bell further and stings the keeper. A hemostatic agent means nothing to an invertebrate and fouls the water. Moving the two healthy animals adds handling stress and leaves the torn one in dirty water, the reverse of the right decision. With optimal water quality the isolated animal's tear usually closes within days. If shrinkage does not stop and melting begins, consult a specialist.

IssuesPoor intake mesh management caused the accident, and the torn animal was returned to the same tank as the others. The isolation setup was available but the owner failed to decide to use it first.

ImprovementMake "isolate first" the rule for injured animals and keep spare saltwater and an isolation container ready at all times. Double the intake mesh, fix it in place and check it daily. Photograph the wound's progress and learn the criteria for recovery versus deterioration.

1 a.m. While cleaning the tank, the owner touched their face with a hand coated in upside-down jellyfish mucus, and the neck and face have turned red and swollen. Ten minutes later hives have spread over the whole body, with a tightening feeling in the throat and difficulty breathing. There is an over-the-counter antihistamine in the house.

Which is the most appropriate first action?

1. Take the over-the-counter antihistamine, lie down and wait until morning
2. Wash the face with seawater and soak in a 40°C bath to draw out the venom
3. Take the jellyfish out of the tank to remove the cause
4. Body-wide hives with breathing difficulty may be anaphylaxis, so call an ambulance immediately

AnswerD. Body-wide hives with breathing difficulty may be anaphylaxis, so call an ambulance immediately

ExplanationUpside-down jellyfish mucus contains clusters of stinging cells that sting on skin contact. Local pain can be handled by rinsing with saltwater and soaking in hot water, but body-wide hives together with throat tightness and breathing difficulty may be anaphylaxis to the venom, and the airway can close within minutes. Call an ambulance immediately and wait in a position that eases breathing. People sensitized by previous stings are at particular risk. An over-the-counter antihistamine does not stop anaphylaxis, and waiting until morning can be fatal. Saltwater rinsing and hot water are local measures and insufficient for a systemic reaction. Removing the jellyfish does not stop the reaction inside the body. Tell the paramedics it is a systemic reaction to jellyfish stinging cells.

IssuesThe owner did not know that upside-down jellyfish sting through their mucus alone and touched their face with a working hand. Working alone late at night, they had not learned in advance the signs of a severe reaction or when to call for emergency help.

ImprovementWear gloves when working with upside-down jellyfish and never touch the face during work. Post the "call an ambulance" signs for stings (body-wide hives, breathing difficulty, throat discomfort, dizziness) on the wall and share them with the family. Anyone who has had a strong reaction to a previous sting should avoid the work.

One of three moon jellyfish has begun melting white from the bell margin, and a third of the bell has broken down in half a day. Pulsing is faint but the mouth and stomach are still intact. The other two are healthy, but the water has become slightly cloudy. It is the middle of the night and no one to consult is open. A small isolation container and spare artificial seawater are available, and salinity and temperature can be matched. Fragments of broken-down tissue are drifting in the water.

Which is the most appropriate judgment?

1. Watch in the same tank until morning and call when someone to consult opens
2. Dispose of the melting animal at once and do a full water change
3. Isolate the melting animal in a separate container of clean saltwater, change water in the main tank to protect the other two, and consult a specialist in the morning with records
4. Cut away the melted part and wait for recovery in the original tank

AnswerC. Isolate the melting animal in a separate container of clean saltwater, change water in the main tank to protect the other two, and consult a specialist in the morning with records

ExplanationMelting that destroys a third of the bell in half a day is fast-moving and threatens the water quality for the others. But as long as the mouth and stomach remain and there is pulsing, recoveries do occur, so disposal is premature. The best that can be done at night is to cup the melting animal into a separate container of clean saltwater at matched salinity and temperature and let it rest, and to siphon out the cloudiness and do a small water change in the main tank to protect the two healthy ones. In the morning, gather the temperature, salinity, ammonia reading and progress photos and consult a specialist. Waiting until morning in the same tank lets the broken-down tissue foul the water and endangers all three. A full water change is a major shock to the healthy animals too. Cutting away the melted part widens the wound and worsens it. If melting continues after isolation and the shape fully collapses, judge it dead and remove it.

IssuesThe owner had not looked up anyone to consult at night and had no plan for dealing with a melting animal. It was also unclear whether the isolation container and spare saltwater were actually ready to use.

ImprovementKeep an isolation container and spare saltwater ready at all times and write down "melting starts = isolate" as the rule. Note the contact details and hours of vets that treat invertebrates, aquariums and the shop. Photograph the daily check so the speed of change can be communicated.