i have a silver mollie in my tank and whenever the air pump is on it goes straight to the bottom and doesn't move that much but when i turn it off he is very active
It's very difficult for us to guess what might be going on, just from the information you've given us.
Could you post some more details of your set up, please? How big is the tank, how long has it been set up, and is it heated and filtered? Exactly what and how many fish are there? How is the tank decorated? Have you tested the water at all?
Sorry for all the questions, but anything else you can tell us will be useful