purple tang

I have this purple tang that is fat, happy, eats non stop. However, he has a small white spot on his left side right next to his dorsal fin near the back. He also has a small patch of them on the right side directly in front of his tail about 1/2" away. They seem to come and go, staying for a week or so at a time. No other fish in the tank have this. Any ideas? The crappy photos I took are hard to make out.
http://photobucket.com/redirect/album?showShareLB=1" target="_blank">http://s1188.photobucket.com/albums...le%20tang/" target="_blank">
http://s1188.photobucket.com/albums...le%20tang/

 

Thanks everyone, he is a handsome fish. I do have a cleaner shrimp in with him. I was just curious more than anything.. He is active and eating and looking good otherwise. I typically don't get too worked up over things such as ich. I just didn't want something too crazy going on as I get ready to bring home my new Achillies Tang!!