How to Clean a Fish Tank...

Step 13 Put the fish back into the aquarium

You have now allowed ample time for the tank to adjust. That means it is time to put your fish back into the tank. Hopefully they are all okay and there were no casualties in the cleaning process. Lift up the lid and light again, bring your fish over in their temporary bowl, and quickly pour all of the water and your fish quickly into the aquarium. Make sure there is room so the tank doesn't overflow. Replace the cover and light, and let the fish adjust to their clean home.

After you pour the fish into the tank, they will be sluggish again, but after a few hours they should be back to normal once again...