Move fish only into a cycled, heated tank with treated water at a matching temperature. Scoop them into a clean plastic container filled two-thirds with old tank water, float it, net them across, and test ammonia daily for a week.
Here’s how to move fish to a new tank. Get the new tank running and cycled first, and match its temperature to the old one. Then net the fish across in a container of their old tank water. Keep the lights off for the rest of the day and test for ammonia daily for a week. Moving fish into an uncycled tank is the mistake that kills them.
Scope: this covers moving fish between two tanks in the same home, such as an upgrade or a hospital tank, plus a few hours of transport. A house move or a long-distance trip is a bigger job. Species differ, so check the needs of what you keep, and see the Fish Care guides. Buying new fish instead? See how to add new fish to a tank.
Before You Move the Fish
- Cycle the new tank first. Fish need bacteria to process their ammonia, and a new tank has none. Follow how to cycle a fish tank, which takes about 4 to 6 weeks, and see how to set up a fish tank for the build.
- Treat the water. Use a conditioner, and remember that some Australian suppliers add chloramine. SA Water says not to add tap water directly to a tank, and to prepare it first.
- Match the temperature. Set the new heater to the same temperature as the old tank, and check both with a thermometer. See what temperature a tropical fish tank should be.
- Carry the bacteria across if you can. Many keepers move a piece of filter media or some old tank water into the new tank, and keep the old filter running until the new one settles.
How to Move Fish to a New Tank Step by Step
You’ll need a soft net and a clean plastic container. See the net roundup.
- Confirm the new tank is ready. Ammonia and nitrite read 0, nitrate is present, and the temperature matches the old tank.
- Dim the room. Turn the lights off on both tanks to keep the fish calm.
- Prepare a container. RSPCA Australia says to use plastic containers that have never held toxic chemicals and are thoroughly washed and dried, filled about two-thirds with aquarium water.
- Catch the fish gently. Use a soft net, move a few at a time, and lift them straight into the container.
- Float the container. Leave it floating in the new tank for up to 30 minutes so the temperature evens out. RSPCA UK gives half an hour for new fish in a bag. With the same treated water at the same temperature, a shorter float is often enough.
- Net the fish into the new tank. Don’t tip the container in, so old water, debris and any disease stay out.
- Leave the lights off for the rest of the day, and skip feeding until the next day.
- Test daily for a week. Check ammonia and nitrite, and read how to reduce ammonia in a fish tank if a reading appears.
How to Move Fish to a New Tank When the Trip Takes Hours
Sometimes the trip is longer than a walk down the hall. RSPCA Australia’s emergency transport guide covers this.
- Water and containers: fill each container about two-thirds with aquarium water.
- Oxygen: run a battery-operated air pump with an air stone, and carry spare batteries.
- Warmth: keep tropical fish in a warm area.
- No food: don’t feed fish in the containers, even over a few days, to keep waste down.
- Checks and limits: open the lid every four to six hours to check the pump, and expect to need a water change after about 36 hours.
In an Australian summer, keep containers out of the sun and out of a hot parked car, because small volumes of water heat up quickly. Watch the temperature the whole way.
Common Mistakes
- Moving fish into an uncycled tank. Ammonia will climb with no bacteria to clear it.
- Using untreated tap water in the new tank. Chlorine and chloramine harm fish.
- Ignoring the temperature gap. A sudden difference stresses fish.
- Using a bucket that held soap or chemicals. Even traces can harm fish.
- Tipping the old water in. It brings debris and, if the fish were sick, disease.
When to Call It
If fish gasp at the surface, hide for several days, or an ammonia reading appears in week one, test the water and change 10 to 25 per cent. RSPCA Australia gives those percentages for a new tank. Ask your aquarium shop or a fish vet if it doesn’t settle.
Related Guides
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Frequently Asked Questions
How long can fish stay in a container while I move them?
For a same-house move, minutes to an hour is plenty. For a longer trip, RSPCA Australia says fish can stay up to about 36 hours in aerated containers before a water change is needed.
Do I need to acclimate fish moving between my own tanks?
Yes, at least for temperature. Float the container for up to 30 minutes, then net the fish across. If both tanks use the same treated water at the same temperature, a shorter float is often enough.
Can I put water from the old tank into the new tank?
Yes, and many keepers do to carry some bacteria across. Use clean water from a healthy tank, not from a tank with sick fish.
Should I move the filter as well?
Moving some filter media helps the new tank’s bacteria, and keeping the old filter running for a while helps more. The new tank still needs to be cycled.
How do I move a betta to a new tank?
The same steps apply, using a small clean container and a matched temperature. Check the Betta Fish guides for care needs.
