What is this?

[Zoofan]

How long has it been there? It looks like a sponge and if on a new rock then it will most likely down off instead of grow unless you are meeting its food requirements.

If it has grown in tank then that is great. I wouldn't worry about it hurting anything. I had a pink one that covered all the branches of a 4 headed Hammer coral. That was a very neat coral.

Mike

[Pennies2Cents]

It just started growing bigger. It was a tiny little circle when we got the rock and now its about 1 inch in diameter. I would say about 5 months ago is when it started.
yes it is in my tank.. I guess I will let it grow. We will soon be upgrading to a 125. we will see what happens then..