The sponge will grow. You should try to get an id on it. Maybe you can actually get a Nudibranch that eats that type of sponge.
Before you do anything though, I would do something about what Deanos is talking about
I am not planning on adding anymore fish. Thanks for the help
Just curious, but why would he go through the trouble of getting a nudibranch to eat something thats perfectly reef safe?
-Kris
I was thinking it would be cool to be able to keep a Nudibranch and actually have it thrive. I have two different sponges and thet grow fast, I am surprised that yours grow slow. Is it bad for them to grow fast? Mine spread onto the neighboring live rocks and actually took over a full piece for themselves.