I've been having these purple dots start to show up on my rocks. At first I thought it was cyano bacteria, but a turkey baster does not blow them away. I went to an LFS last night, and they seemed to think that they are a form of colonial hydroids, and mentioned I could treat it with fenbendazole. All the pictures I see online show colonial hydroids as having tentacles with fans at the end. These just look like little polyps. Wanted to get other thoughts, as if I go down that path, it sounds like will be a good amount of work removing snails and anomenes to keep safe.