Introducing new fish correctly: step by step to a stress-free start

Buying new fish is always a special moment. For the joy to last, the first few hours are crucial: transport and moving into a new tank are very stressful for the animals. With the right approach, the start can still be gentle – and at the same time you protect your existing fish.

Before buying: good preparation is half the battle

Is the aquarium ready?

New fish should only go into a cycled aquarium. A newly set-up tank lacks the bacteria that convert toxic waste products such as nitrite. Wait until nitrite is no longer detectable – this usually takes a few weeks.

Are the fish compatible?

Before buying, find out about the size, temperament and requirements of the species you want. Do the water parameters, especially hardness, match? Is the tank large enough? Will the new fish get along with your existing stock?

Never keep shoaling fish alone

Many popular aquarium fish such as tetras, rasboras or Corydoras catfish live in groups and only feel comfortable in a shoal. The Swiss Animal Welfare Ordinance also requires that animals of social species are given appropriate contact with others of their kind. So plan a suitable group size from the start.

Stock gradually

Do not add all the fish at once. Each new inhabitant increases the load on the water. Stocking in several stages gives the filter bacteria time to adapt.

Transport home

Fish are usually transported in bags with water and air. Take them home as directly as possible and protect them from cold, heat and bright light – an insulated bag or polystyrene box is ideal. Darkness also calms the animals.

Acclimatisation step by step

1. Switch off the light: a darkened aquarium reduces stress for new and existing fish.
2. Equalise the temperature: place the closed bag on the water surface for about 15 to 20 minutes so that the temperatures can equalise.
3. Mix the water slowly: open the bag and add small amounts of aquarium water every few minutes. Over 30 to 60 minutes, the fish gradually get used to the new water parameters. This step is especially important when hardness or pH differ greatly.
4. Transfer the fish: catch the fish out of the bag with a net and place them in the aquarium. The transport water should not get into the tank, as it may contain pathogens and pollutants.
5. Allow rest: leave the light off for the rest of the day and do not feed at all, or only very little, on the first day.

Good to know: after a long transport, ammonium can build up in the bag. As soon as the bag is opened and the water comes into contact with air, the pH rises and ammonium can turn into toxic ammonia. For very long transport times, it is therefore advisable to carry out the acclimatisation fairly quickly after opening.

Quarantine: safety for all your fish

Even fish that appear healthy can carry pathogens. A separate quarantine tank in which new fish spend two to four weeks is therefore the safest solution. There they can be observed calmly and treated if necessary, without endangering the rest of your stock. A small tank with a heater, filter and a few hiding places is perfectly sufficient.

The first weeks in their new home

• Observe their behaviour: are the new fish eating? Are they swimming normally?
• Check the nitrite level during the first few days, especially after larger additions.
• Watch out for territorial disputes or fish being chased and intervene if necessary.
• If signs of disease appear, act early.

A good start pays off

A little patience when introducing new fish is worth it: the animals settle in faster, stay healthy and soon show their full colours. At the same time, you protect your existing fish from introduced diseases.

At AQUATANA we offer everything you need for a safe start – from water conditioners and bacterial starters to nets, water tests and complete sets for a quarantine tank. We are also happy to advise you on compatibility and suitable stocking for your aquarium. Visit our online shop and give your new fish the perfect welcome.