Red patchy area around left eye

A

aqua_man

Guest
I have a yellow tang which I have had in my tank for a little over 2 months. I haven't introduced any new fish for awhile now, and I find today he is scratching his left eye area on rocks, and letting the cleaner shrimp clean this area.
Does anyone know what this could be? I'm not sure if the skin is coming away or if its just color.
 
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