I just got my first live rock a week ago, and found a crab right away. Last night, I saw some kind of slug, and this morning there was a little sea star! It's not a serpent or brittle star. This is one of the more bulky stars. I know that the brittles and serpents eat detritus, and algae. What about the fatter ones? Also, there are these little bug looking critters swimming around on the glass and substrate. The look almost like tiny beetles, and they're about a millimeter long. Are these bad?