How to Acclimate New Aquarium Fish: Float and Drip Methods
Photo by scazon on Openverse (CC BY 2.0)
To acclimate new aquarium fish, float the sealed bag in your tank for 15-30 minutes so the temperatures match, then slowly mix in your tank water over 30-60 minutes so the fish adjusts to the new pH and hardness. Finally, net the fish into the tank and discard the bag water. Never pour the store water into your aquarium.
Acclimation is the process of letting a new fish adjust gradually to the temperature and water chemistry of its new home. Store or shipping water is almost always a different temperature, pH, and hardness than your tank, and dropping a fish straight in forces it to absorb that change all at once. That shock, not the trip itself, is what kills most new arrivals in the first 24 hours.
Why acclimating fish matters
Fish constantly balance the salts and water moving across their gills and skin, a process called osmoregulation. A sudden jump in pH, temperature, or salinity overwhelms that system and causes osmotic shock, which can be fatal even when the fish looked fine in the bag.
There is a second, quieter risk. During transport, a fish sits in a closed bag where waste builds up as ammonia. As long as the water stays acidic and cool, most of that ammonia remains in its less-toxic form. The moment you raise the pH by mixing in your tank water too fast, that ammonia can turn toxic. Slow acclimation, plus discarding the bag water, sidesteps both problems.
What you need
- A clean bucket or container used only for aquarium water
- A length of airline tubing (for the drip method)
- An air valve or a loose knot to control the drip rate
- A soft net
The float method (temperature only)
The float method matches temperature and takes about 20 minutes. It is enough for hardy fish coming from a local store with similar water.
1. Turn off the aquarium lights. Dim conditions calm the fish and reduce stress.
2. Float the sealed bag. Let the unopened bag float on the surface for 15-30 minutes so the water inside reaches your tank temperature.
3. Net the fish across. Open the bag, gently net the fish into the tank, and discard the bag water down the sink.
The drip method (temperature and chemistry)
The drip method matches both temperature and water chemistry and is the safest option for shrimp, wild-caught fish, saltwater livestock, and anything shipped a long distance. Plan on 45-60 minutes.
1. Empty the bag into a bucket. Pour the fish and its water into a clean bucket set below the tank. Tilt the bucket if needed so the fish stays fully submerged.
2. Start a siphon with airline tubing. Run airline tubing from the tank to the bucket and start a gentle siphon. Tie a loose knot in the tubing, or use an air valve, to slow the flow to about 2-4 drips per second.
3. Drip until the volume doubles. Let the tank water drip in until the water in the bucket has roughly doubled. This slow blend is what gives the fish time to adjust to your pH and hardness.
4. Discard half and repeat if needed. For very sensitive species, pour out half the bucket and drip again until it doubles a second time.
5. Net the fish into the tank. Move the fish with a net, never by pouring, so none of the bucket water enters your aquarium.
How long should you acclimate fish?
Match the time to how different your water is from the source and how sensitive the species is.
- Hardy community fish from a local store: 20-30 minutes; the float method is usually enough.
- Shipped fish or unknown water chemistry: 45-60 minutes with the drip method.
- Shrimp, snails, and wild-caught fish: 1-2 hours on a slow drip.
- Saltwater fish and corals: at least 45-60 minutes by drip; check parameters as you go.
Common acclimation mistakes to avoid
The biggest mistake is pouring the bag or bucket water into your tank. That water can carry ammonia, disease, and parasites, so always move the fish with a net. Two more to avoid: acclimating with the lights on, which adds stress, and skipping quarantine. Whenever possible, acclimate new fish into a separate quarantine tank for two to four weeks before they meet your existing fish, so an unnoticed illness never reaches the main tank.
It also helps to prepare before the fish arrives. Make sure the tank is fully cycled, the water temperature is stable and correct for the species, and that you have room for another fish. If you are still deciding what to add, our guide on choosing the right fish for your aquarium can help you avoid an impulse buy that does not fit.
Should you do a salt dip during acclimation?
For most home aquarists, a plain, careful acclimation is all you need. Some keepers add a brief bath for freshwater fish arriving from a questionable source, but that is an optional extra step with its own risks. If you want to understand when a bath helps and how to dose it, read our guide to using aquarium salt with freshwater fish before you try it.
Frequently asked questions
How long should you acclimate new fish?+
Allow 20-30 minutes for hardy fish from a local store using the float method, and 45-60 minutes for shipped fish or sensitive species using the drip method. Shrimp, snails, and wild-caught fish benefit from a slow 1-2 hour drip. The bigger the difference between the two waters, the longer you should take.
Can I put the bag water into my tank?+
No. Bag water can carry built-up ammonia, disease, and parasites from the store or shipping. Always net the fish into your tank and discard the bag water. This is one of the most important rules of safe acclimation.
What is the drip acclimation method?+
The drip method uses airline tubing to slowly drip tank water into a bucket holding the new fish and its original water, at about 2-4 drips per second, until the volume doubles over 45-60 minutes. It gradually matches the fish to your tank temperature, pH, and hardness, and is the gentlest option for sensitive species.
Do I need to acclimate fish if the water looks the same?+
Yes. Water that looks identical can differ sharply in pH, hardness, and temperature, and those invisible differences cause osmotic shock. Even fish from a nearby store should be floated for temperature and, ideally, drip-acclimated for chemistry.
Should the aquarium lights be on or off during acclimation?+
Turn the lights off. New fish are already stressed from transport, and dim conditions keep them calmer while they adjust. Leave the lights off for a few hours after you release them, too.
