Whats wrong with my fish ??

[janalta]

Don't add more Prime than the recommended dose. Just add it to the new water you mix up before the water change.

What kind of airation do you have in the tank now? Is there a lot of water flow ( powerheads) ?
If not...a lack of O2 and low gas exchange could be part of the problem.
An airstone won't hurt....but you will need a more permanent solution...such as additional powerheads if this is the case