I'm not sure what this is actually called. The LFS where I got it calls it Branching GSP. I think it is a Corky Sea Finger. Either way it is growing in leaps an bounds. Two months ago when I put it in my tank it was abt 1 1/2 inches tall it is now abt 4 inches and adding two arms. I also notice that a hard black base is forming. Is that base normal?