I have a sick angel who is about 5 years old. For the past week he has been sitting on the bottom either upright or lying on his side. He looks pretty bad but is still regularly eating, every time he sees me walk into the room he bolts up to the top. However, whenever he swims he seems like he is weighed down, something is up with his swim bladder. The only other thing is very mild fin melting, not obvious unless you look very closely. My first thought with swim bladder / finrot is water quality, but it is fine, 0 ammonia and nitrite, about 25 ppm nitrate (planted). I ran a course of Erythromycin but it hasn't helped him yet. Any advice? He's still eating so that's good, but I don't know what else I can do to help him.