Hi, im new to salt tanks and bought a leather coral, it is attatched to a small live rock. There are these round fan things that pop in and out of the live rock. Just want to make sure they are a wanted tank item and not anything that is a pest.
Tube worms are good, they count as "clean up crew" in my books, they take gunk and other things out of the water and eat it (like all filter feeders). The only spread if there is enough food for them, but its not a bad thing as agian they clean the water and are a sign of a healthey reef if they survive.