Difficult to tell from the pic, is the base dissolving or is there algae growing on the base? If it's dissolving the best course of action is to remove and frag it, if it's algae growth be sure your flow is appropriate. How is your polyp extension? Anything in the tank possibly picking at it?
It's not dissolving. The polyps come out but not the entire way. I've never seen anything by it and the yellowish white color seems to be moving up closer to the top of it. I put more flow on it