Yellow Tang needs help

[cnaugh]

Can someone tell me what this is?
It's like he is turning black around his gills and eyes. The pics really do not do it Justice. He, along with all my others are in a hospital tank now getting copper safe treatments.

 

[Dav3]

Are the fins rotting away?

 

[cnaugh]

No, I thought of that also but I really don't see any rot. I'm afraid I may have really screwed up. I did a freshwater dip and he is not looking to great. Not sure if he will make it through the night.