How do you add fish to a fish tank with fish?

Float the bag from the pet store in the tank for 30 minutes to acclimate the temperature. Then begin removing water from the bag by dipping it out with a small cup. As you dip, discard the pet store water, and replace it with the same amount of aquarium water. The idea is to slowly acclimate your fish to the water chemistry of your tank, but not allow any water from the pet store to enter your aquarium. Pet store water is often contaminated with disease. The water acclimation should be done for 1/2 hour, with each dip removing no more than an ounce or two of water from the floating bag and replacing it with an equal amount.

Once the fish have been acclimated to your aquarium water, take the bag out of the tank, and pour fish and water through a net. Quickly get them into their new home. Again, you do not want pet store water to enter your tank. Pouring into a bucket is a good idea because it will catch jumping fish that may leap from the bag past the net. You can net them from the safety bucket and complete the transfer.