Help w/a schooling bannerfish

It's just that my trio of schooling bannerfish have been pecking on my green mandarinfish male lately. I know that the bannerfish are cleaner fish so could there be anything on the male? I did see a few bumps on his skin... One of the bannerfish (the oldest of the crew, though they're all juvenile) developed black spots on his face. It isn't black ich though... it looks more like cells underneath his skin have turned black. There's a black blotch on the top of his fin too, and it's slowly getting bigger. Help, anyone?
FlameAngelfish:goldfish: