It seems that my Hippo Tang has an eroded face, like it's degenerated. He swims normally, eats like a pig, and nothing else seems to be wrong. It is just that his face is almost eroded away. And my Purple Tang has a similar case with a thin white line going across his body. His face is fine and he also swims normally and eats like a pig. Can anyone identify these disease and give me a form of treatment?