it kinda sounds like aptasia. where did you get it? if you got it from aquatic warehouse they have been having some aptasia problems by the looks of their tanks. I would suggest a copperband butterfly (if your tank is big enough) and /or a few peppermint shrimp. depending on how many there are you might want to try squirting joes juice on them0. squirting boiling water on them works, can probably kill other fish , and harm some other corals... I have some aptasia (i can't see them but i found two the other day), i used the boiling water method and now they are gone. but I'm afraid they spread so I picked up a peppermint shrimp from the lfs, and I hope he will take care of any other stray ones the will pop up, and till they eventually are all whiped out. all these solutions are only good if it is aptasia. Do you think you can post a pic? if you need any more help pm me.