FAQ: Health for fish

KH acts as a buffer that stops pH changing suddenly. When KH is very low, pH can drop quickly, especially in a tank with infrequent water changes, and a sudden pH crash stresses fish and can even kill them.

A fish's body temperature follows the water, so in water that is too cold its immunity and digestion slow, while warmer water holds less oxygen and speeds up metabolism. Keep the temperature right for the species and avoid sudden swings.

Switch off the lights, open the lid, aim a fan at the water surface and increase aeration, because warm water holds less oxygen. Cool it gradually: do not tip in ice or cold water suddenly, as a temperature jump harms fish.

Fit a working heater as soon as possible and let the water warm gradually, not suddenly. Until then, wrap or cover the tank with a blanket. When a heater fails, also check that it did not overheat the water beforehand.

Use a thermostatic heater sized for the tank and glance at the thermometer every day. Do not place the tank near a radiator, window or air conditioner, and use water of the same temperature for water changes.

The chlorine and chloramine used to disinfect tap water damage fish gills and skin and kill beneficial filter bacteria. So every time, an aquarium water conditioner must be added to new water as the label directs.

Yes, copper in particular, which can come from old pipes or some products, is very harmful to shrimp and snails and in larger amounts to fish. Many water conditioners bind heavy metals, and it is worth running the tap for a while before filling.

Fish gather at the surface, gasp or breathe quickly, especially in the morning, because at night plants and bacteria only use oxygen. Oxygen runs short more often in warm, overstocked tanks or where the water surface does not move.

An air pump helps when the tank holds many fish, the water is warm, the surface barely moves or fish are being treated, since some medications reduce oxygen. In many tanks a filter whose outflow ripples the surface is enough.

Long-finned fish such as bettas or fancy goldfish struggle in strong current, tire and become stressed. You can soften the flow by aiming it at the glass, putting a sponge over the outlet or choosing a weaker filter.

With too many fish the water fouls faster, oxygen can run short, aggression and stress increase and diseases spread faster. When deciding how many fish to keep, consider their adult size, behaviour and the filter's capacity.

Usually not, because a sudden change in every parameter stresses sick fish even more and removes some of the beneficial bacteria too. Partial changes are more often recommended. In case of acute poisoning, ask a specialist urgently about a larger change.

Insect sprays, air fresheners, paint, varnish or smoke can reach the water through the air and poison fish. When using such products, cover the tank, switch off the air pump or move its intake, and ventilate the room well.

Fish medications are usually grouped by what they target: parasites, bacterial or fungal infections, and some act more broadly. Because similar signs can have different causes, it is worth consulting a vet before choosing a product.

It is not recommended. The wrong medication will not help, can put extra strain on the fish and upset the tank's balance while the real disease progresses. Test the water first and see a vet so the cause can be identified.

Look for a vet clinic that works with exotic animals or fish; some vets also consult from photos or videos. Experienced aquarist communities are useful too, but a vet decides on medication and treatment.

Useful details are the tank volume, water test results and temperature, which fish and how many live there, when and which signs appeared, whether new fish or plants were added recently, what you feed and whether you have used any products. Clear photos and a video help too.

Poor water quality is very often the cause of fish problems, and then medication does not help until the water is fixed. Weakened fish in bad water also cope with treatment less well. Sometimes signs disappear once the water improves.

Follow the label or the vet's instructions strictly, dose according to the real water volume, finish the whole course and watch the fish during treatment. Before treating, check whether the product suits your fish, plants and invertebrates.

Activated carbon absorbs many medications, so they stop working as intended. It is usually taken out during treatment and can be used afterwards to remove medication residue. Exact instructions are usually on the medication label.