Welcome to Aquaria Central! You will find wealths of info here! Does the little dots look kinda like grains of salt or lice? If so it is a common disease called ich (which puffers and tangs are notorious for coming down with). What other tankmates do you have and what size tank and what are the water quality readings (ammonia, pH, nitrite, nitrate, specific gravity). If it is ich, then other fish can get it if equally stressed (ich comes from stress is kind of like a flu or cold for humans). If you have some garlic it wouldn't hurt soaking their food in garlic as ich can't/won't attatch as well to the fish. Anyway hope this helps and good luck and welcome to AC!