Marine fish

Marine ich (Cryptocaryon)

SignsFine white spots on the body, rubbing against rocks, rapid breathing, loss of appetite

PreventionAlways quarantine new fish in a separate tank for 2–4 weeks. Avoid sudden changes in temperature or water quality

Trichodina infection

SignsBody surface looks cloudy white and slimy, rapid breathing, rapid weakening

PreventionAvoid overcrowding and buildup of organic waste. Keep the water clean with a protein skimmer

Marine velvet (Amyloodinium)

SignsFine gold-dust-like coating on the body, extremely rapid gill breathing, death within days

PreventionIntroducing fish via a quarantine tank is the best prevention. Never return an affected fish to the main tank

Vibriosis

SignsRed ulcers and bleeding on the body, fin loss, cloudy eyes, swollen belly

PreventionKeep nitrate low; avoid fights and sharp rocks that cause wounds

Lymphocystis

SignsWhite cauliflower-like lumps on fins or body; appetite remains

PreventionViral. Triggered by stress and poor water quality. Often resolves on its own if the water is kept clean

Weakening from high nitrate / low pH

SignsDull color, staying still in a corner, spitting out food, clamped fins

PreventionTest nitrate and pH (8.1–8.4) weekly and change 1/4 of the water with artificial seawater

Fight wounds between the same species

PreventionClownfish as a pair only; damselfish singly or in a large tank. Introduce fish at the same time

First aidMove the weaker fish to an isolation box. Keep the seawater clean and wait for fins to regrow. If it ulcerates, start treatment

Sea anemone stings

PreventionDo not house anemones with fish that are not their symbiotic hosts. Keep fish away when moving an anemone

First aidIsolate the stung fish and observe. If white patches appear, keep the water clean to prevent secondary infection

Live rock collapse

PreventionStack rocks securely and reinforce with adhesive or rods. Do not place rocks directly on sand that fish dig in

First aidAfter a collapse, check fish for injuries and the water for cloudiness. If a fish is trapped, lift the rock gently to free it

Jumping out and drying

PreventionA lid is a must. Tangs and anthias jump when startled. Turn lights off gradually at night

First aidReturn to seawater and hold it so flow passes through the mouth and gills. Add slime-coat protectant at the labeled dose. Keep dark and quiet for a few hours

Nontuberculous mycobacterial infection

RouteThrough cuts on the hands via tank water or live rock

PreventionWear rubber gloves for live rock work. Wash hands with soap afterward

Vibrio infection

RouteEnters wounds from seawater or fish spine punctures

PreventionDo not put your hands in the water if you have a cut. See a doctor if it turns red and swollen

Palytoxin poisoning

RouteHandling corals (zoanthids/button polyps) bare-handed or with boiling water

PreventionNever boil or pour hot water on corals. Never touch them bare-handed

Salmonellosis

RouteHand-to-mouth after touching tank water or substrate

PreventionDo not pour tank water down the kitchen sink. Wash hands thoroughly

Food

• Marine fish pellets/flakes 2–3 times a day, an amount eaten within minutes
• Supplement with frozen brine shrimp and copepods
• Give tangs plant matter such as seaweed sheets daily

Water

• Mix artificial seawater to specific gravity 1.021–1.025 and aerate 24 hours before use
• Top off evaporation with RO or purified water (adding seawater raises specific gravity)

Toys & play

• Holes and tunnels in live rock serve as playground and refuge
• For clownfish, an anemone or an alternative hiding place
• Strong light and moderate flow bring out natural behavior

Nest, bed & hideout

• Create more hiding holes in live rock than there are fish
• Always provide rock shelter for resting at night

Bedding & litter

• Spread a thin layer of coral sand to maintain pH
• Siphon only the surface of the substrate at water changes
• In a bare-bottom tank, siphon out waste daily

Cage / housing material

Glass tank, skimmer, heater, chiller, hydrometer/refractometer, water test kits

Size & space

60 cm (60 L) or larger. Even for small fish, more water volume means more stability

Layout

• Secure live rock and create swimming routes and hiding holes
• Ensure oxygen and flow with a skimmer and pumps
• Use a heater with a guard so fish cannot touch it

Placement notes

• A dedicated stand that tolerates salt creep and weight, plus waterproofing
• Avoid direct sunlight; it causes algae and overheating

Exercise, free-roam & walks

• No walks needed. Balance swimming space with hiding places
• Observe every fish's breathing and body surface at daily feeding
• Do not chase with a net. Catch with a container or trap

Temperature & humidity

Temperature24–26°C. A chiller is essential in summer; above 28°C is dangerous

HumidityNot applicable underwater. Use a lid to limit evaporation and specific gravity swings

Summer & winter

• Summer: keep at or below 26°C with a chiller or fan. Use ice packs during power outages
• Winter: run two heaters in case one fails, and keep the room warm too

Nail trimming

No nail trimming. Instead, check specific gravity and temperature daily and test nitrate, pH and KH weekly

Brushing, skin & coat care

No coat care. To protect the slime coat, never touch the fish; keeping the water clean is the best care

Other care

Clean the skimmer cup weekly. Rinse filter media in seawater. Wipe salt creep frequently

Protection from predators

• Use a heavy lid and placement so cats cannot reach the tank
• Beware of predation by large tankmates, crabs and mantis shrimp
• Prevent jump-outs caused by sudden lights-out at night

Foreign-body ingestion

Fish swallowing small coral sand is usually harmless, but match food size to the mouth. People should beware of venomous creatures in live rock

Being stepped on

Watch your feet so you do not step on a fish that jumped onto the floor during tank work. Return a fallen fish to seawater immediately

Getting pinched

Fish get stuck in pump intakes, skimmers and rock gaps. Fit a sponge on intakes, secure rocks and manage gaps

Falls

Tank tipping or collapse is the biggest accident. Total weight can exceed 100 kg; use a dedicated stand and anti-seismic mat

Escape

A lid is essential to prevent jumping. Tangs, anthias and wrasses are especially prone. If found on the floor, return it to seawater even if dry

Safe release procedure

1. Separate fighters with a divider or isolation box
2. Isolate the fish being chased first
3. Rearrange the rocks to reset territories
4. Reintroduce simultaneously with the lights dimmed

After the release

If a spine cuts you, wash under running water and disinfect; see a doctor if it swells. For the fish, keep the water clean and wait for healing

What to tell the vet & what to bring

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

Checking consciousness, breathing & heartbeat

• Whether and how fast the gills move (normal is a calm, steady rhythm)
• Escape response when you bring your eyes or body close
• Even on its side, if the gills move there is room for recovery

Stopping bleeding

• Minor bleeding stops with rest in clean seawater
• Add slime-coat protectant at the labeled dose to prevent secondary infection
• If bleeding continues or ulcerates, see a vet who treats fish

Transport

• Double-bag in tank water with plenty of air
• Insulate in a foam box, keep dark, do not shake, and keep the trip short