Those black dots are more than likely Black Ick. Black ick is very natorious in Yellow Tangs- especially ones brought in from parts of Hawaii. It is not lethal by itself, but it can stress the fish which opens opportunites for other diseases. It is also contagious. One method of treating it, I have heard is using a Formalin freshwater bath. Sorry I can't help to much with curing it, but finding out what it is, is a step in the right direction. I'm sure others wll have some more info.
[ October 22, 2001: Message edited by: -Shawn- ]