Every morning when I go and look at my fish tank, I notice that my tangs are completely covered with ick. Usually by the afternoon I notice ick is no longer on the body, and the colors of the tangs are back to normal. FYI... I have the very fine white sand in my tank. It can't be the white sand, since I have a wrasse who sleeps in the sand and by morning it has no white spots on its body. Is this normal for tangs to go through or what can it be? What do I need to do.