My pictus catfish has been swelling up over these past few days. His belly looked like it was housing a marble last night, and this morning it like like a walnut! He is swimming in place against the glass, which is normal, but his belly is so distended that im getting really worried. I don't think its a disease like dropsy, as I recently added 4 panda barbs to the tank and they're not sick, neither are any of my other fish. He still seems to eat, but his belly is so huge! any suggestions on what i should do? thanks.