Been noticing perfectly round white spots left in the coralline algae everyday. Almost the size of my yellow tangs mouth. Figured it was the yellow tang rasping the coralline off since there isn't much algae for it to eat. Last night I spotted the culprit though. An asterina starfish, fairly large too. Explains why the white spots got bigger. I don't seem to have a lot though. I guess the coral banded shrimp does a good job of eating any small critters.