FAQ: Supplies for fish

Used aquarium water can go down the drain, and water without medication can be used for houseplants or the garden, as it contains nutrients. Never release aquarium fish, plants or snails into natural waters.

Released aquarium fish, plants or invertebrates can spread disease and become invasive species that harm local wildlife. If you cannot keep a fish, give it to another fishkeeper or ask at a pet shop.

Fish themselves rarely cause allergies, but some people react to dry food, especially dried daphnia or bloodworms. If you notice symptoms, talk to a doctor and choose a different food.

Dose exactly according to the label, do not mix different products unless necessary, and keep them in their original containers out of children’s reach. When treating fish with medication, activated carbon usually has to be removed from the filter, as it absorbs the medicine.

Warning signs are a fish that stops eating, hides, keeps its fins clamped, gasps at the surface, rubs against objects, or develops white spots, a film or sores. Test the water first, as many diseases start with poor water quality.

It usually points to a lack of oxygen or poor water quality, such as raised ammonia or nitrite. Increase aeration, test the water and change some of it; if things do not improve, consult a vet who knows fish.

Remove the dead fish as soon as possible so it does not rot and pollute the water. Check the water parameters and temperature, look over the other fish, and if several die in a row, contact a vet who knows fish or an experienced fishkeeper.

Yes, some vets advise on aquarium and pond fish, though there are fewer of them than vets for dogs or cats. They can help find the cause of illness and advise on treatment, so it is worth finding one in advance.

It is a small separate tank with a filter, a heater and a hiding place, used for new or sick fish. It helps if its filter is already established, for example by using a sponge that has spent some time in the main tank.

Most important are stable, clean water, the right temperature, moderate and varied feeding, a tank that is not overcrowded and quarantine for new fish. Stress from unsuitable tankmates or sudden changes weakens the fish’s immunity.

Aquarium salt is sometimes used as a supporting measure for certain freshwater fish, but many species, plants and invertebrates are sensitive to it. Before using any treatment, follow the label and consult a vet who knows fish.

Colours fade due to stress, poor water quality, illness, unsuitable lighting or a one-sided diet. Fish are also naturally paler at night, just after being introduced or when frightened.

Occasional rubbing can be normal, but frequent rubbing may signal irritation from water quality or parasites. Test the water and inspect the fish, and if you see spots or a film, consult a vet.

Moving a sick fish to a quarantine tank is often advised so the disease does not spread and the fish is easier to watch. Some diseases have already spread through the whole tank, so it is worth consulting a specialist about treatment.

In spring the fish’s immunity is still weak after winter, while parasites and bacteria become active sooner in the warming water. So at this time it is important not to overfeed, to look after the filter and to watch the fish’s behaviour.

Water conditioner, water tests, a spare heater, an air pump, a net, a separate bucket and a small quarantine tank are useful. Medicines are best chosen with a vet once you know what needs treating.

A marine tank needs marine salt, a refractometer to measure salinity, stronger flow and often a protein skimmer. It is more demanding and more costly to set up, so beginners are usually advised to start with freshwater.

It is usually not recommended, because nitrate, phosphate and silicate in tap water encourage algae in a marine tank. Marine tanks normally use RO water mixed with marine salt.

It is a marine aquarium device that uses fine air bubbles to remove organic matter from the water before it breaks down. It helps keep the water clean, especially in tanks with corals.

It is porous rock that hosts beneficial bacteria and small organisms, so it acts as a biological filter. Dry rock is also an option and becomes colonised by bacteria later, but the tank then takes longer to settle.