FAQ: Health for fish

It is food containing an active ingredient, mostly used for internal diseases, because the medicine goes straight into the fish's gut. It only works if the fish is still eating. Whether this treatment is suitable is worth discussing with a vet.

In a small tank even a slight error means a large overdose, so accurate dosing matters especially. Use a precise measuring tool and follow the label, and if the stated dose does not suit a small volume, ask a vet rather than guess.

No. Many medications should be diluted in tank water first and poured into the filter outflow or where water mixes quickly, away from the fish. This spreads the medicine evenly and keeps the fish out of an overly concentrated zone.

UV light can break down the active ingredients of some medications, making them less effective. Whether to switch the steriliser off during treatment is usually stated on the medication label.

Specialists sometimes recommend a slight temperature rise as part of treatment, but it does not suit every species or disease, and warmer water holds less oxygen. Do not do it on your own: consult a vet and raise the temperature only gradually.

Partial water changes remove nitrates, organic matter and other build-up that cause constant stress and weaken fish immunity. Stable, clean water lowers the chance that the microorganisms always present in a tank will cause disease.

When water goes unchanged for a long time, its parameters drift and the fish adapt to them. A sudden large change with fresh water then causes a sharp shift that can be dangerous for the fish. After a long gap, change smaller amounts several times in a row.

Cyanobacteria smother plants and substrate, and oxygen drops as they decay. Some types can release toxins, especially in ponds during heavy blooms. They are worth removing by hand, improving water quality and watching how the fish are doing.

They can. Some products harm sensitive fish, shrimp or plants, and algae that die off quickly use up oxygen as they rot. If you use such a product, follow the label, increase aeration and watch the fish.

When decorations are moved often, fish lose their usual hiding places and territories and get stressed, and disturbed substrate clouds the water and releases dirt. Rearrange rarely, and if you must, do it a little at a time.

Yes, especially if it was used in a tank where fish were sick. Wash a used tank and equipment, disinfect with an aquarium-safe product as the label directs, rinse well and let them dry, and preferably replace the filter media with new.

Many commercially bred fish adapt to moderately hard water, but for some soft-water species hard water causes long-term stress and hinders breeding. It is easiest to choose fish that suit your water, or to soften it gradually after talking to an experienced aquarist.

Yes. Sharp or coarse substrate can damage the barbels and bellies of bottom dwellers such as corydoras, especially if the bottom is dirty. Sand or fine rounded gravel that you clean regularly suits them better.

In the cold season room temperature fluctuates more, especially when heating goes on or off, and the heater works harder and can fail. Airing the room can also chill the tank. Watch the thermometer more closely at that time of year.

Common reasons are a neighbour overfeeding, a failed or clogged filter, heating trouble or water left unchanged for a long time. When you get back, test the water, clear leftovers and change part of the water, and consult a specialist if the fish behave unusually.

A fish's body is covered by a slime layer that protects it from pathogens and helps regulate its water balance. Dry hands, cloth or a rough net damage it, so fish should be handled as little as possible and, if needed, with wet hands or a container.

Most popular tropical aquarium fish do well at about 24–27 °C, but needs vary by species. Check the recommended range for your fish and choose tank mates that suit a similar temperature.

Coldwater fish such as goldfish are usually fine at room temperature, so a heater is not essential. Sudden temperature swings still harm them, though, so keep the tank away from radiators, windows and direct sun.

Lifespan depends heavily on the species: some small fish live a few years, while goldfish or larger cichlids can live over a decade in good conditions. Water quality, the right tank size, diet and low stress matter most for longevity.

If the fish is still alive, return it to the tank quickly with wet hands or a container and let it recover quietly in dim light. Watch it for a few days for wounds or signs of infection, and fit a lid on the tank.