FAQ: Health for fish

Painted or varnished items, non-aquarium plastics, metal parts that rust or release copper, and material from nature that may carry pollutants can all be unsafe. Choose decorations made for aquariums and rinse them before adding them.

Yes, limestone rocks, shells or coral pieces slowly raise water hardness and pH. That suits cichlids from hard-water lakes but not soft-water fish. You can test a rock with a few drops of vinegar: if it fizzes, it contains lime.

New items can carry manufacturing, packaging or storage residues, dust or oil. So rinse decorations, hoses and equipment in clean water without detergent before adding them, and watch the fish more closely for a few days afterwards.

Suitable, varied and moderate feeding strengthens immunity, colour and resistance to disease. Overfeeding fouls the water and causes digestive problems, while a monotonous diet can lead to nutrient shortfalls over time. Choose food suited to the species.

Most adult aquarium fish are usually fed once or twice a day, as much as they eat within a few minutes. Fry need smaller portions more often, while some species, such as predators, are fed less often. Follow recommendations for your species.

Uneaten food rots and raises ammonia, fuels algae and clouds the water. The fish themselves can become overweight from oversized portions, and their digestion or swim bladder can suffer. Overfeeding is one of the most common causes of aquarium problems.

Most fish fed quality, varied food need no extra vitamins. Supplements are sometimes used for recovering fish or conditioning for breeding, but use them as labelled and do not let them replace a complete diet.

Many aquarists do this with healthy adult fish, as a fasting day lets the gut empty and reduces water pollution. Do not fast fry or young fish this way, since they need food often.

Yes, live food collected from natural waters in particular can carry parasites and pathogens. It is safer to use live food from reliable sources or cultured at home, or frozen food, which is often additionally treated.

Thaw frozen food in a small container of tank water, pour off the thawing liquid and feed only what the fish eat. Do not refreeze thawed food or keep it for long, as it spoils quickly.

Vitamins in opened food break down over time, and moisture can cause mould. Keep food tightly closed in a dry, cool place and choose a pack size you will use within a few months.

Many goldfish keepers choose sinking pellets or soak dry food before feeding so the fish gulp less air at the surface. Not overfeeding and adding plant-based foods to the diet also matter.

Offer a sick fish small portions of easily digested food it likes, and remove uneaten food quickly so it does not foul the water. If the fish has eaten nothing for several days, tell the vet.

Bottom dwellers often miss out on food that other fish eat at the surface. Give them sinking food after lights out or in the evening when most other fish are resting. Watch that the bottom dwellers do not lose weight.

No. Bread and other human food are unsuitable for fish digestion, swell and rot quickly and foul the water. Feed only food made for fish, and give vegetables such as blanched courgette only to species they suit.

Bettas need warm water at a stable temperature, gentle flow and clean water, because their long fins are sensitive to poor water quality. Males are usually kept singly, and fin-nipping fish should be avoided as tank mates.

The commonest causes are poor water, too low a temperature, strong flow or nipping, and sometimes the betta bites its own fins. Check the water and temperature and change water more often, and see a specialist if the fins keep deteriorating.

Goldfish grow large and produce a lot of waste, so in a small tank waste builds up and water quality drops quickly. They need a roomy tank, a strong filter and frequent water changes, which prevents many water-related health problems.

In spring fish immunity wakes up more slowly than pathogens do, so it is a vulnerable time. Feed gradually and sparingly as the water warms, clear out built-up leaves and sludge, start the filter and watch the fish closely.

The commonest causes are a pond too shallow, which freezes to the bottom, and a fully frozen surface under which decay gases build up and oxygen runs short. Enough depth, leaves cleared in autumn and an ice-free spot on the surface help.