Hi,\nMy live rock appears to have lots of dark blue/purple sponge growing on them. The sponge like to grow on the least lit area of the rock. I think its sponge...it looks lightly raised, soft and velvetty. Alittle slimmy smooth to the touch. Even abit like a fungus type...small and some have a eye type mouth. Are they harmless? I know they dont live long...can they cause swings in levels? How do you get them under control if you have lots?