The Easy Way to Acclimate Reef Tank Fish

Clownfish. swimming in a coral
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    There are several ways to acclimate a new fish to a reef tank. They can vary from the simple to the highly-complex. In this article we are going to highlight a simple method to acclimate a new fish.

    Acclimation overview

    The two most popular methods of acclimating a new reef tank fish are the “floating bag method” and the “drip method”. Most reef tank experts would agree that the “best” method would be the “drip method” as this very gradually introduces the new fish to the reef tank water. However, many reef tank owners like the “floating bag” method because you don’t need any special equipment, it is often quicker, and it works perfectly well for the vast majority of fish.

    Note: When considering how to acclimate your fish, it is recommended that you consult with your LFS(Local Fish Store) to see if your new fish would suit a particular acclimation method, just to be on the safe side.

    What you will need to acclimate

    This is what you will need in order to use the floating bag method:

    1. Small container / measuring cup (1/2 cup is ideal)
    2. Peg (or any method to stop the bag from moving/sinking)
    3. Medium / Large bowl
    4. Fish net

    The Floating Bag method

    1. Un-open the fish bag a little and place it in the tank for 15 minutes

    This allows the temperature between the water in the fish bag and the reef tank to equalize. By opening the bag a little, fresh oxygen is introduced into the bag. If you find your fish bag sinking or moving around your tank, use a peg to affix it to the side of your tank. Alternatively, if your reef tank has a lid you can probably trap the top of the bag under the lid which will have the same effect. Allow around fifteen minutes for this phase.

    2. Using the small container / measuring cup, add 1/2 a cup of tank water slowly into the bag

    Try and do this gently so as not to scare your new fish.

    3. At 5-minute intervals, add another 1/2 cup of tank water

    4. When the fish bag becomes full, remove around 50% of the water from the bag and empty it into the bowl

    Use your judgment as to how full your bag is. Don’t let the bag become too full as it may be difficult to keep in place at the top of your tank. Removing 50% of the water doesn’t have to be exact, again, just use your best judgment.

    5. Repeat steps 3 and 4 until around 45 minutes have passed

    6. Test the water in the bag

    This is often considered an optional step. But, if you have your test kit on hand, it may be worth at least testing the water for salinity and Ph etc. The aim of this is to have the test results match as closely as possible between the reef tank water and the fish bag water.

    7. Using the fish net, catch the fish and put it into your tank

    The fish is probably quite stressed already, so it’s very important to do this part slowly and carefully.

    8. Dispose of the fish bag and water from the bowl

    Throughout this whole process take care not to get any of the water from the fish bag or bowl into your tank.


    During the acclimate process, your fish will probably be stressed, so it’s a good idea to keep the tank lights off (or on low) for the rest of the day. Alternatively, add your new fish in the evening. The darkness of the tank results in a calmer environment for your new fish, and your other tank occupants will also be calmer resulting in there being less chance of them harassing your new fish.

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