encrusting something?

[adamjay]

I have had a brown spot on my live rock ever since I got it about 2 years ago. Since then, it has been growing bigger and encrusting over the rock and up the wall. It seems slippery to the touch and I have peeled pieces off but it will not come all the way off. I looks and feels like some sort of algea. My tang doesn't eat it and I don't want it to overtake my coralline algea and make my tank brown. There are no hairs it is just a flat encrusting mat. I have no pictures at this time. Does anyone know what it is? What can I do.

Adam

 

[sammystingray]

Maybe a sponge? Do you see any openings? How about maybe something that looks like veins (water canals)? Even upon very close inspection...you still see no type of polyps such as a porite?