My fish will only stay at the surface of the water. If he swims down he immediately floats back up to the surface, like if he were swimming around in salt water and just can't seem to NOT float. The other concerning thing is that he floats tilted off to one side, so he's half on his side. He spends most of his time up against the side of the tank to help keep himself upright.
I'm concerned he will die soon, and hasn't been eating his normal ferocious amount in the last few days.
Any ideas of what my fish has or how I could possibly cure him?