[Myka]

Does it get tiny, fuzzy hairs/filaments on it sometimes/often? If so, it's Pseudolithoderma sp. I think I can see the filaments - tough to say the filaments are very, very fine. It used to be called Ralfsia sp. but the name was changed - you can find more pics under this old name than the new one.

This is what Julian Sprung says about it, I've the same experience:

"It is a brown seaweed that adheres tightly to rock and other solid surfaces. The filaments are a sign that it is growing and healthy. This is, in my opinion, as desirable alga, quite like various coralline algae. A strong growth of it usually indicates good water quality. I can't imagine why you would want to remove it!

If you wanted to curb its growth and encourage more diversity of corallines, you might try adding one Diadema urchin. Otherwise leave it alone.

Sincerely,

Julian Sprung"