I just noticed this on my common pleco. On his left fin there is a blister like growth or something. I already have coppersafe in the tank that was put in two weeks or so ago. I have added more water (changed the water.) Should I put some more in it? He stays in a cave with a lace catfish and chased my pictus catfish out of the cave but they really don't fight. Here are some pictures. It looks like a big blister and I don't know how long he has had it. Sorry the pictures are blury. What could this be? I don't have a hospital tank. Everything in the tank seems to be normal. None of the other fish have this.
