A lady I know was downsizing so i took her reef tank and added it to my collection haha. She told me these things are hydroids. She obviously didn't keep the tank cleaned like it needed to be, it's definitely an ongoing project to get it right. They have long tubs and fuzzy type tops that disappear kinda like feather dusters. They are seeded pretty deep in the rock. Any one have suggestions on how to get rid of them, at this point I'll do about anything.. it's nearly impossible to pick them out one by one.