looks like a zoanthid muncher to me.
look at night for more on your polyps, as well as little white sprials of eggs on the sides fo the polyps when closed. brush them with soemthing to make them close up for easier inspection. They also tend to take on the color of the polyps they are eating at the time...so if yours are pinkish colored....I would look at your pink polyps first.
montipora munchers are tiny....here are pics of both...the second pic is of monti munchers and those nudis are abotu the size of just the head of the first pic of the zoa munchers
could be where they started....)
