How to Properly Introduce New Fish to the Tank


After you’ve carefully chosen just the right collection of fish to add to your fish tank, you’ll want to make sure that you introduce them to the water and possibly other fish properly.  How sad it would be for a child if just hours after the excitement of possibly their first pet, the fish turned up dead from simply not acclimating them to their new home correctly.  One of the reasons why there is a need to properly introduce fish to an aquarium is the bacteria content.  Simply mixing pet store fish tank water with clean aquarium water makes for an unhealthy environment for the fish.

Fish can go through a shock process when moved from one tank to another, so be sure to follow each of these steps gently and with patience.

When starting a new aquarium, the most important step in the process is to set everything up, including the water, and let it set for 2-3 days.  This will help to stabilize the new environment.  Also when dealing with a new tank, it’s important to start out with only one or two fish per week.  This will allow the eco-system to develop slowly and the proper bacteria to grow naturally.

When you bring your fish home from a pet store, they will be in a clear plastic bag filled with water from their original tank.

  • Turn off the fish tank light, as the fish will be calmer in a darker atmosphere
  • Carefully place the plastic bag in the water of your fish tank, and let it float for about 15 minutes.  This will allow the water in the bag to acclimate with the temperature of the water in the tank.
  • If you already have fish in the tank, let the bag float for about 25 minutes, giving that extra 10 minutes for the fish to become “introduced” to each other.

A new aquarium requires a certain amount of live bacteria that can be purchased at the time you get your fish at the pet store.  Bacteria are important to the health of the fish because it prevents the water from becoming toxic by processing the fish waste.  You will not need to add bacteria to the water each time you add fish, just when it is a new tank.

After floating the bag of new fish in the water, it is time to release them into their new environment!

  • Open the plastic bag and put a cup of water from the tank into the bag and wait a few minutes, just to mix the water and let the fish adjust to it.
  • Open the bag again and slowly turn it upside down, letting the fish swim into their new home.  Make sure to pour all of the water out of the bag into the tank.
  • Watch your new fish for about 10 minutes, and then you can turn the tank light on.

Now all you have to do is watch and enjoy as your new aquarium comes to life!


  1. The reasons given for acclimation are not quite accurate. Differences in temperature and pH are the primary reasons that fish die from shock, and this is why one acclimates fish.
    Lack of biological filtration from too few bacteria are the reasons that fish die from ammonia toxicity; typical for new tank syndrome. It takes 4-6 weeks for bacteria in the tank to increase enough in new systems to process the ammonia generated by the fish. Ammonia is toxic at low levels.

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