FAQ: Health for fish

Some medications reduce oxygen in the water, and sick fish need more oxygen, especially if their gills are damaged. An extra air stone or more surface movement helps the fish cope with treatment.

Many fish medications, especially those containing copper, are very dangerous for shrimp, snails and other invertebrates. Read the label before treating, and move invertebrates to another tank or treat the fish in a separate tank.

Some medications and salt can harm sensitive plants, whose leaves may then melt or rot. Whether a product suits a planted tank is usually stated on the label. During treatment, remove rotting plant parts so they do not foul the water.

Yes, some medications, especially antibacterial ones, can harm beneficial filter bacteria, so ammonia and nitrite may rise during treatment. Test the water regularly during treatment and do partial changes if the medication instructions allow.

Not without a vet's instruction. Medications can interact, increase each other's toxicity or weaken their effect, putting extra strain on the fish. If one treatment did not help, consult a specialist before starting another.

Yes, stick to the duration on the label or given by the vet. Signs can disappear before the pathogens do, and stopping too early can let the disease come back and be harder to beat.

Common reasons are a wrongly identified cause, poor water, activated carbon left in the filter, a miscalculated water volume, or treatment started too late or stopped early. In that case do not switch medications yourself; consult a vet.

Medications are dosed by water volume, and the real volume is less than the tank's stated size because of gravel, rocks and an unfilled top. Dosing by the nominal volume can mean an overdose, so calculate by the water height and subtract what decorations take up.

Not on your own. Human medicines are not made for an aquatic environment, their effect and dosing differ for fish, and misuse can harm the fish and filter bacteria and promote resistance. Ask a vet about treatment.

In the European Union, antibiotics for animals, fish included, are generally only available on a vet's prescription. This is to make sure they are used only when truly needed and to limit bacterial resistance. See a vet about antibiotic treatment.

Keep them in their original packaging, tightly closed, in a cool, dark place out of reach of children and pets, as the label directs. Do not decant medications into other containers, so they are not confused with other products.

No. The effectiveness and safety of expired medications are no longer guaranteed: they may not work or may be harmful. Take unusable medications to a pharmacy or waste collection point rather than pouring them down the drain or into nature.

Wear gloves when handling medications, protect your eyes and skin, and wash your hands afterwards. Measure with a separate container used only for that, and keep medications away from food and out of children's reach.

Some fish medications contain dyes, so the water, silicone seams, decorations or plastic parts can be stained. The water colour usually clears after water changes and carbon filtration once treatment ends, but silicone sometimes stays tinted.

After the course, unless the label says otherwise, do several partial water changes, put activated carbon in the filter to absorb residues and test ammonia and nitrite for a few days. Return shrimp and snails only once the medication residue has been removed.

It depends on the disease. Contagious diseases often affect every fish in the tank even if only one shows signs, while a non-contagious problem or injury is better treated separately. It is worth deciding together with a vet.

Some aquarists use aquarium salt as a supporting measure, for example to ease fish stress after transport or as part of treatment on a specialist's advice. It does not suit every species and should not be used constantly without reason.

Ordinary table salt often contains iodine and anti-caking agents that are unwanted in an aquarium. If salt is used, choose salt made for aquariums or pure salt with no additives, and use it only as a specialist recommends and the label directs.

Freshwater aquarium salt is usually plain sodium chloride used as a supporting measure. Marine salt is a complex mix of minerals designed to recreate seawater. They cannot be substituted for each other.

Scaleless or fine-scaled fish, such as many catfish, and some soft-water species are often more sensitive to salt. Shrimp, snails and many plants are sensitive too. Check about your species before using salt.