Help, Yellow Tang has tiny black dots on its body

[Delphinus]

Sounds like black ich or black spot disease, pretty common on yellow tangs at first.

It's a flatworm, and very effectively treatable with a freshwater dip. Match the temperature and pH of your tank water, catch the fish and put him in FW for, I think, about 4 minutes. The flatworms will fall off. In extreme cases you may need a second FW dip in a week or so but when I had to treat a yellow tang I only needed to do it once.

http://saltaquarium.about.com/cs/com...a/aa041701.htm

People talk about using formalin in the FW dip. I found I didn't need to but your mileage may vary.

Good luck.