Probably ick. Try posting in the disease forum, you could get more info on curing it there. You can also do a search for the disease. And do you have a quarantine or hospital tank to use? If so, put him in there.
ok ur fish is gonna most probobly gonna die because u havnt been reading much n u got one of most easy dieses catching fish should hav gotten da powder brown aka whitefaced tang
sorry sudsy I had to learn the hard way too. I had a yellow tang and a blue tang both get ick and the blue died. I didn't do enough reaserch to learn that tangs get ick as much as people get allergies. Well maybe not that bad but it's still pretty bad. Not that I'm an expert or anything but I'd just stay away from tangs. And stress at all freaks em out.