My betta used to be happy. I've had him for over five months now. He lived with me at college, then we took him home and he moved from a small tank to a large, 10 gal one. When I went back to college he came, but his water got nasty because the filter broke. So we got him a new tank (the bio wanted the 10 gal) and he's in a 3 gallon one now. The water is clean, it has a heater, and a filter.
He hasn't been eating for a long time. His back is curved drastically and he looks as if he's just wasting away. I'm very worried about him. He also has black scales all around his front, which used to be blue. His fins are also looking mottled. He mostly lies at the bottom of the aquarium, and it looks as if he is panting. What is wrong?