Acclimatising new fish
The size of the difference matters more than the method. Where shop water and tank water are similar, floating the bag for temperature and then netting the fish across is enough. Where they differ substantially — particularly in hardness, TDS or pH — a slower drip is worthwhile, and it is essential for invertebrates.
Short answer
Adjusting a new arrival gradually from the transport water to the tank water, so the change in temperature and chemistry is not a shock.
Method
- Float the sealed bag for fifteen to twenty minutes to equalise temperature.
- For fish, net them out and add them to the tank. Do not pour shop water into your tank.
- For shrimp and other invertebrates, drip tank water into a container holding the animals over about an hour, until the volume has roughly trebled.
- Dim the lights and leave the tank alone for a few hours afterwards.
Why not pour the bag in
Transport water contains accumulated ammonia, and it is at whatever pH the bag has drifted to. Opening the bag lets CO₂ escape, pH rises, and ammonium converts to toxic ammonia — which is why a long acclimation with the bag open can be worse than a short one. Net the fish across and discard the water.