They are aptasia. They spread very quickly. I had them bad. I used a product called Joes juice. I found it can harm my corals though. I got some peppermint shrimp because they eat the aptasia. I haven't seen a single one since I got them. I would highly recommend getting the shrimp before using any treatment.New tank and after a fews days this appeared. Seems to recess into a tube at night? Any thoughts? I want to make sure it's not bad for my tank. Thanks!View attachment 294297