I just read this on liveaquaria.com:
In the tank, it needs a varied diet high in beta-carotene and vitamin C, and low in protein matter. To maintain its bright coloration, however, it must keep to a strict herbivore diet to prevent fading. Therefore, the diet of the Yellow Hawaiian Tang should consist of dried and frozen herbivore food that contains marine algae, and vegetarian items such as Spirulina, zucchini, broccoli, leaf lettuce, and dried seaweed.
What are you feeding your yellow tang currently?
, I'm not sure about the little dots, I'm sure somebody on here will know more about that