I've got one piece of live rock in particular (although all are affected) that looks like someone has dumped a full vacuum cleaner bag of dust on top of it. I mean, if this was an end table, it would be like not dusting for a couple of months. What is it exactly? Can I clean it off or should I leave it on there? It doesn't seem to be a problem except for the fact that its probably covering up some pretty coraline algae.