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Acclimating New Aquarium Fish

The importance of properly acclimating new aquarium fish.

By David A. Lass |

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One of the most overlooked and important aspects of fishkeeping is how you acclimate new aquarium fish to an existing tank. Many aquarium fish that were perfectly fine at the local fish store have met untimely ends in hobbyists' tanks due to improper acclimation.

What is Acclimation?
Whenever I have gone from the cold north in the winter to higher climates in Florida or the Caribbean, or from sea level up to higher altitudes, it took me a little while to get used to the differences. The same is true with our fish, and whenever they are moved from one tank into another, they need to be gradually acclimated to the new water conditions. This is true whether the fish have been shipped from far away, or if you are moving them from one tank in your house to another. The most important water parameters that the fish need to be acclimated to are temperature, pH and nitrates level.

Acclimating New Fish
There are a number of methods for acclimating new aquarium fish to a tank, and this is how I do it. This does not mean that this is the only way to do it, or that there are not other good ways. First, float the bags the new fish come in in the tank for 10 minutes -- no more. Next put the new fish and the bag water they came in into a container that will hold about four times the amount of water that is in the fish bags. Make sure that this container is one that is dedicated ONLY to use with your fish tank(s), and make sure there has never been any soap in it. Put the fish and the bag water they are in into the container. Then, every couple of minutes over a half hour period, take some water from the tank the fish will be going into and put this water into the container. The water added from the tank to the container (each time) should be about 20 percent of the amount of water in the container from the fish bags. After half an hour, net the fish out of the container and put it into your tank. Dispose of all of the water in the container. It is very important to observe your fish for as long as possible after introducing them into their new tank, as you want to make sure they are not getting picked on by the existing inmates in the aquarium.

Quarantine Tanks
To start with, everyone should have a quarantine tank, and all new fish should spend two to three weeks in the quarantine tank before being introduced into the main fish tank. This is to make sure that the new fish are not carrying any disease or parasites. The quarantine tank can be a simple 5 or 10 gallon tank, and all you need is a sponge filter that has been in a tank with fish, so it is "charged" with the good bacteria of the nitrogen cycle, a heater, a cover and a light. If you want to treat the new fish as a preventative, give them a couple of doses of Quick-Cure (formalin and malachite green). Observe the fish every day during the quarantine period, and when you are sure they are not carrying any disease or parasites, you can put them into the main tank, using the method described above. Use the same acclimation process for introducing new fish to the quarantine tank, and from quarantine to main tank.

Water Change
You should do a 25 to 30 percent water change before introducing new fish to the tank. The reason is that, depending on the filter you have, if you don't do regular water changes the nitrates in your tank have probably built up to high levels. Fish can handle high nitrates if they have been accustomed to the high levels over a long period of time. The problem happens when you take fish from low nitrates, which will be the case in most tanks at most good local fish stores, and you plunk them into high nitrate conditions. If the nitrates in the tank they are going into are too high, this could stress and even kill the new fish. This is why local fish stores usually ask for a sample of your water if you have had their fish die shortly after being introduced into your tanks. The store wants to make sure that they are not simply sending replacement fish into a high nitrates tank to perish.

Bottom Line
Please take the small amount of time and effort required to acclimate fish. It will prevent many common problems.

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Reader Comments

Renee    Garden City, MI

3/18/2014 10:52:28 AM

Excellent article for a beginner like myself.

Eric    Raleigh, NC

4/4/2013 2:23:39 PM

Thanks for taking the time to post. Great info in a short article. Just what the doctor ordered.

Saundra    Inglewood, CA

7/17/2011 11:16:24 PM

much needed info

ethan    brownsville, TX

11/4/2010 11:44:22 AM

good read

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