Is it receding, or just closing up? Regardless, it isn't happy. Mine don't like a ton of light and like low to medium flow. Are your parameters in check? Alk and Ca are the most overlooked killers in a reef aquarium. How long have you had it? What kind of lighting and how much flow? I'd recommend putting it low in the tank with subdued flow to see what it's going to do for you (good advice for anything new to a tank, unless you're talking acros from under MH to under PC's, etc.). Once it starts to look good again, start moving it around to find the best spot for the tank, but give it a number of days between moves to acclimate to the new spot.