A week ago my goldfish started floating upside down. I didn't feed him for two days, and then on the third day I started feeding him peas (just a 1/4 of a pea per day..he's a small fish). Then a few later he started sinking, he had a very difficult time getting to the surface. Now, as of two days ago, he sits on the bottom and can't swim very well. He still eats very well, I have to hand feed him b/c he doesn't have enough strenght to swim to the top of the tank. I checked all of the parameters and everything is normal. What should I do??