I've had a common plec for 5 years who has always had skin blisters. Posted in here years ago and subsequently treated him with just about everything from melafix to maracyn with no effect. None of the other fish in the same tank have ever been affected. He's in with various loaches, a large frontosa and a blue ahli all of which remain healthy. Here is an updated picture of the plec. I'd be interested if anyone has any ideas.
