I have 3 that I have bought and 2 that came as hitchikers. I have noticed I don't need to do anything for them. They scavenge the algaes and really seem to love eating the Coraline algae. I have 2 pencil urchins, 2 pincushions, and one that I think is a rock boring urchin, don't know the actual name for it though. The pincushions are my favorite as they are always out and about where as the pencils only come out at night, and i hardly ever see the rock boring urchin.