How to acclimate new fish

Why acclimate?

New fish arrive in water that differs in temperature, pH, and hardness from your tank. Sudden changes cause stress and can shock or kill fish. Acclimating lets them adjust gradually.

Float the bag

Turn off the tank light to reduce stress. Float the sealed bag on the water surface for 15–20 minutes so temperatures equalise. Don’t let tank water into the bag yet. If the bag is small or the fish are large, use a bucket of tank water and float the bag in that.

Drip acclimation (optional but better)

For sensitive or expensive fish, use a drip: pour bag water and fish into a clean bucket, then run a thin tube from the tank so water drips in slowly (2–4 drips per second). Over 30–60 minutes the water in the bucket matches the tank. Then net the fish into the tank — don’t pour the bag or bucket water in, to avoid introducing store water or ammonia. Our drip acclimation guide has full step-by-step instructions.

After adding fish

Give the fish time to hide and settle. Avoid feeding for the first few hours. Keep an eye on water parameters; adding fish can cause a small ammonia or nitrite bump if the tank is new or heavily stocked. Use App-aquatic to log tests and reminders.

Quick takeaways

• Float the bag 15–20 minutes to match temperature.
• Drip acclimate for sensitive species (30–60 minutes).
• Net fish into the tank; don’t pour store water in.
• No feeding for a few hours; monitor parameters after adding fish.