3,895 answers about fish & aquatics
A healthy aquarium is a balanced one — water chemistry, filtration, stocking and feeding all work together, and most fish problems start with the water. This page gathers the fish and aquatics library of KinsLe Answers in one place, organized by topic for freshwater and saltwater keepers alike. Every answer is original, written by KinsLe, and tied to a real KinsLe feature.
273 answers in Health & Vet Care — page 7 of 12
Fast, laboured breathing with flared gills means your fish's gills are struggling to pull enough oxygen from the water or are irritated and swollen. Low dissolved oxygen, ammonia burning the gill tissue, nitrite in the water and gill parasites all produce this picture, and several fish showing it at once points first…
Clear water can still be dangerous water, because the things that kill fish fastest — ammonia and nitrite — are completely invisible. A sudden death with no warning often traces to an ammonia or nitrite spike from an overfed or still-cycling tank, chlorine from an untreated water change, or an overnight oxygen crash…
KH is carbonate hardness — the water's buffering reserve, which is what stops pH swinging dangerously between morning and night. GH is general hardness — the calcium and magnesium dissolved in the water, which fish and shrimp use for bones, shells and basic body chemistry. Fish suffer when either value sits far from…
Zebra danios are famously tough, so illness in one is worth taking seriously: a fish that thins to a bent, hollow look while the school stays fat often carries a slow internal infection, and older danios commonly develop curved spines as they age. Watch for the fine gold dusting of velvet under a torch, white spot…
Siamese algae eaters are robust workers, and most of their problems are circumstantial: white spot after a rough journey or cold change, torn fins and stress when kept singly or crowded with lookalike species they spar with, and a slow thinning when the algae runs out and nobody feeds the fish that was bought to feed…
Pearl gouramis usually stay healthy for years, then fail in recognisable ways: thread-like droppings and a thinning body from internal parasites, red sores opening on the flanks, fins rotting back, and laboured surface breathing when the water's surface film or low oxygen makes their air-breathing organ work too hard.…
Kuhli loaches have no true scales, which makes their skin their weak point: white spot takes hold fast, bacterial patches spread quickly, and medications that scaled fish shrug off can damage them at full strength. A healthy kuhli is plump and glossy with bold bands; warning signs are bands fading, the body thinning…
Harlequin rasboras are hardy when settled, and their illnesses usually arrive with change: new fish, a cold water change, a stressed journey home. The signs are the school itself — one fish leaving the triangle-marked group, colour draining from the copper body, scratching against leaves, or a fine gold dusting…
Guppies fail fast and visibly: tails that melt or split, a grey-white film spreading from the saddle area behind the head, and fish that waste away while still eating. Red thread-like worms protruding from the vent are a parasite that spreads through the whole tank and needs prompt attention. Bent spines and shrunken…
Buoyancy trouble tops the goldfish list: floating tail-up, sinking to the bottom, or rolling after meals, especially in round-bodied fancy varieties whose organs are compressed by their shape. Also watch for split or reddened fins, a pinecone-lifted scale pattern which signals a serious internal problem, white spot,…
Corydoras advertise their health through their barbels: whiskers worn down to stubs mean the gravel is too sharp or the bed is dirty, and infection quickly follows. Watch too for rapid breathing and dashing to the surface more often than the species' normal occasional gulp, frayed fins, white spot, and a fish…
The emergency that defines cherry shrimp keeping is the failed moult: a shrimp trapped in its old shell, sometimes showing a pale band around its middle, because the water's mineral balance no longer lets it build or shed a shell properly. Beyond that, watch for shrimp turning milky white inside the body, dark rusty…
The troubles that catch bristlenose plecos out are mostly gut and skin problems: constipation and bloat when the diet drifts too rich in protein and too low in fibre, white spot after a temperature swing, and a sunken belly when a shy fish is quietly outcompeted for food. Check weekly that the belly looks gently…
Watch for white spots or a dusty coating on the fins, clamped fins and loss of appetite, long pale stringy faeces, and sores or a swollen belly — angelfish are particularly prone to parasitic problems, and a fish that stops claiming its usual spot in the pecking order is often unwell before it looks it. New arrivals…
Treat it as an emergency when a fish is gasping at the surface, lying on its side unable to right itself, bleeding, pineconing with raised scales, or when several fish change behaviour at once — a whole tank acting strangely usually means the water, not the fish, is in trouble. Test ammonia, nitrite, and temperature…
In a warm, oxygen-starved filter, the nitrifying colony starts dying back within a few hours, and after roughly a day without flow a large share of it is usually lost, though media that stays wet and cool survives far longer than media left to dry out. When power returns, do not rinse the media in tap water; instead…
Start with the methods that cannot poison invertebrates: siphon out visible pests during water changes, cut feeding so pest populations lose their food supply, add a glass planaria trap baited overnight, and house any fish that hunts pests only if it will not also hunt your shrimp. Read any treatment label…
Bag the fish in a strong fish bag one-third filled with its own tank water and two-thirds air, double-bagged with the inner bag's corners taped or inverted so the fish cannot trap itself, then place it in a dark, insulated box where it cannot roll or get cold. Travel promptly, keep the box out of direct sun and…
Give the fish quiet, stability, and easy food: keep the lights dimmed, hold back tank mates that nip or compete, and keep the water exceptionally clean with gentle, frequent small changes, because a recovering fish's immune system is easily tipped back by ammonia or a temperature wobble. Offer small, appetising meals…
Start by finding the cause rather than chasing the number: test your tap water after it has stood overnight, check whether soft water with low carbonate hardness is letting acids from waste and driftwood pull the pH down between water changes, and rule out a new rock or substrate pushing it up. Smaller, more frequent…
Look after lights-out with a torch along the glass: planaria are flat, arrow-headed worms that glide smoothly over surfaces, while hydra are tiny stalked polyps with a crown of tentacles that wave in the current and shrink when touched. A few hydra are mostly a nuisance, but both can hunt baby shrimp, and planaria…
Move some of the established filter's media — a sponge, ceramic rings, or a chunk of floss — straight into the new filter, keeping it wet in tank water the whole time, because the nitrifying bacteria live on those surfaces rather than in the water itself. Run the new filter alongside fish only once it is processing…
Record every test the same way, on one line: the date, ammonia, nitrite, nitrate, pH and temperature, plus a few words of context such as a filter clean, a new fish or a feeding change, because a number without its story explains very little later. Test at a consistent moment, ideally just before your weekly water…
Zebra danios are hardy enough that quarantine can be simple, but simple is not the same as optional: new danios occasionally arrive carrying spot diseases or with a thin, wasting look that only shows against a few quiet weeks of feeding. A small tank with a snug lid, because danios jump with real commitment, a gentle…
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