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Successfully Introducing New Fish to Your Old Established Tank

Updated on March 23, 2013

Choose your new fish carefully to avoid mayhem!

Title: Pirahna ~ License: sxu license ~ Photographer: soundman99:
Title: Pirahna ~ License: sxu license ~ Photographer: soundman99:

Select Your Fish Carefully!

Beginning aquarists often start out with a wild mix of fish that don’t get along. That - along with improper tank set-up - is one of the main reasons new aquariums often fail. Once you have your tank properly set up and seasoned and have weathered the initial problems with incompatible fish or fish that just don’t make it for one reason or other, you may find yourself with a tank that has only a few fish that get along well, and you may want to add a few more. Here’s how:

Do your research! Check out my other fish care articles using the links at the end of this article.

Once you have done your research and determined what types of fish would be likely to get along with the fish you have, take a trip to your local fish store. If you do not already have a bottle of the product, Melafix, at home, get some while you are at the fish store. This is an all natural “tonic” that helps with fish stress. It has a pleasant distinctive smell that, I believe, may help keep the fish from realizing new fish have been added.

Select the type and number of fish you want. Bear in mind that you will not want to introduce a lot of new fish at once. This will tend to stir up aggression as well as causing an ammonia spike in the chemistry of your water. This is bad for all of your fish. A good general rule is to have at least a gallon of tank per inch of fish. So don’t put any more fish in your tank than the number that will equal this equation. If you have schooling fish, it is a good idea to get more schooling fish of the same or a similar type. Get fish that are about the same size as the ones you have now. Avoid getting an aggressive fish to add to your tank.

Plan to do a partial water change when you get home with your new fish. Put a couple of gallons of water from the tank into a clean bucket (one that is only used for fish purposes.) Float your new fish, in their bag, in this water for about 10 minutes to get their water to the same temperature as the water in the bucket, then release them into the bucket.

While they are acclimating to the new water, clean and rearrange your tank. Vacuum your gravel and move all of the ornaments and plants around. Take out some old ones and add some new ones if you can. This will confuse your fish and disrupt their habitual hiding places. This should help keep them from being too territorial. Add new water to the tank. Add a dose of Melafix.

Net your new fish by positioning a large net over a clean, empty bucket and gently pouring the water from the bucket that holds your new fish through the net. By doing this, you avoid chasing them around in the bucket and stressing them even more than they already are. Once they are netted, gently introduce them to the tank.

You will be very tempted to stay and watch them and to check on them frequently, but I advise against this. Instead, turn off the light, cover the tank with a blanket or towel, turn off the room light if possible, and leave them alone overnight. If it is dark in the tank, your fish will all go to sleep and wake up the next day in a completely rearranged tank with no territory marked. This will level the playing field so that all of the fish, new and old, can start fresh.


Do the Math!

I always use Melafix for ponds in my fish tanks because it is highly concentrated and more economical. 1 teaspoonful treats 50 gallons when introducing new fish. 2 teaspoonfuls treats 50 gallons when treating injury or illness. It takes 60 drops to equal a teaspoon, so you would use 3 drops per gallon when introducing new fish and 6 drops per gallon when treating injury or illness. When introducing new fish, treat daily for 3 days, then do a quarter tank partial water change. When treating injury or illness, treat daily for a week and do a quarter tank partial water change. Repeat this process if necessary.


Submit a Comment

  • justmesuzanne profile image

    justmesuzanne 4 years ago from Texas

    Thanks! Yes, at one time I had 17 tanks! Oddly, I have never done well with neons, though. :)

  • Peggy W profile image

    Peggy Woods 4 years ago from Houston, Texas

    Hi Suzanne,

    You certainly seem to know your fish and all about operating a successful aquarium. I love seeing schooling fish like neons. They are so pretty! Up and useful votes.

  • justmesuzanne profile image

    justmesuzanne 6 years ago from Texas

    Good! Glad I could help! Thanks for your comment! :)

  • DRG Da Real Grinc profile image

    Felix J Hernandez 6 years ago from All over the USA

    I don't have fish nor a tank but my room mate does and I will let him know about this Hub because he seems to be getting it all wrong. Whenever he buys new fish there is conflict and then one eventually dies fast.