There is a large button polyp rock in my dad's tank. Most of them are not opening up and there is a white powdery substance or residue on the closed heads of the polyps. Is this a fungus or something else? The water parameters of the tank are normal..but since it is not my tank I do not know all the specifics. Everything else in the tank (mushrooms, ricordias,Kenya tree, fish...all look great.) Any advice would be appreciated and make my dad's Christmas a lot better! 
-J
-J