The Best Way To Acclimate Fish

So you've brought your new fish home and now need to acclimate it. How do you acclimate fish? Well, fish are as sensitive as humans to sudden changes in water temperature. Have you ever been in a hot shower and had the water turn cold on you? You probably didn't enjoy it. Your new fish may do worse than not enjoy the change in temperature. Disease, ich or death can occur if you don't take the time to acclimate your fish properly. Go slow. It's very easy to do.

acclimate.jpgYou'll first want to distract any other fish you may have in the aquarium by feeding them. Turn off the light in the fish tank and float your bag containing the new fish in the water for a 1/2 hour. Make sure the bag is still tightly sealed! This will slowly acclimate the water in the bag to the water in your fish tank.

The next step is introducing the aquarium water. I've found the best way to do this is by placing the bag in your fish bucket with some of the aquarium water. You can leave it in your fish tank, but watch for jumping fish (I had a yoyo loach leap from the bag on to the floor once!), or a bag that rolls. You don't want to add the pet store water to your aquarium.  (Please note:  I use the fishless cycling technique when initially adding fish.  A reader saw that I had a lot of bags in the picture, and thought I was adding too many at once.)

Add 1/3 of the aquarium water to your bag water. By using the bucket you just dip it in a little. Wait 10 minutes, then add a 1/3 more. After 10 more minutes your new fish should be acclimated. The slower you do this process the better. Take about 45 minutes to an hour when you acclimate saltwater fish. Net the fish and place him in your aquarium.

You've avoided mixing the fish store water with your tank water and the fish is acclimated to his new home.

4 thoughts on “The Best Way To Acclimate Fish”

  1. Hi Conor!

    Hey. Thanks for pointing that out. Yes, in the picture I did add many fish at once. I should have mentioned that I use the “fishless cycling” technique to cycle my tank. By using this method, I introduce ammonia into the tank before any fish are added. It allows Nitrosomonas bacteria to grow. They turn the harmful ammonia into Nitrite. Nitrite is still deadly to fish though, but fortunately Nitrobacter bacteria grow. They in turn, eat the nitrite, producing nitrate. In small amounts, Nitrate is fish friendly.

    I believe fishless cycling is the best way to prepare an aquarium for fish. Your bacteria are already present when you introduce your fish to the tank. This avoids them having to struggle, and possibly die.

    I have added 13 fish at once with this method. They were all very happy. I’ve never lost a fish using this method.

    Read my fishless cycling experience in the category “fishless cycling” here at

  2. How do you know you have enough bacteria to handle 13 Fish? that’s why you need to add them slowly.

  3. You don’t need to add them slowly if you use the “fishless cycling” method. This aquarium was new. I had no fish in the tank. It’s actually easier on the fish, because they enter an environment with the good bacteria already there. It’s been a few years, but it took like 6-8 weeks to cycle. I know it was ok, because tho load of ammonia I added was much stronger than the fish could have produced.

    If I was adding fish to an established aquarium, I could not do that method, and would have to add them slowly. Example: If I had 2 fish, and was going to add 10 more.

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