Like I said it's tough to tell from the pictures but I would make sure he is being fed very well and continue to monitor him. Mine developed what looks to be almost identical to yours and it was due to getting scrapped up.
This is what I feed mine daily
http://www.marinedepot.com/ps_ViewItem.aspx?idProduct=HL1121&child=HL1123 she would eat a whole sheet if I let her
I also feed PE Mysis, pellets, rods food, blood worms Cyclop-eeze, reef roids. I mix it up throughout the week with the exception of the seaweed. That is a daily staple in my tank. The cyclop-eeze and the reef roids I roll up in the seaweed tight like a cigarette so they are eating it as they are biting off pieces of the seaweed. Whatever they don't eat by tearing at it, gets mixed in the tank for the corals and pods.