Help ! Flame Angel Not Well

[DiverDude]

I added a Flame Angel to my tank on April 1. He's always been shy and I'm planning on re-aquascaping so he doesn't have quite so many places to hide.

4-5 days ago, I noticed his coulour was off a bit. This morning when I shut the Koralias off to feed, he came out and paraded around a bit and I got a really good look at him and he's definately not well. He's pale and has some kind of skin issue. It appears like his mucus is rough (he's not got his usual sheen) and slightly milky and isn't adhering to his body as it would normally. I don't think it's ich but it does have a white-ish powdery sort of look to it.

He's eating but he seems a slightly lethargic.

Thoughts ?