So, as some of you may know, my tank is under the good care of my girlfriend for 6 (3 to go) weeks while I'm down in sunny Alabama. Before I left I had a bunch of pineapple sponges growing, but apparently, since I've been there, they've grown prolifically. According to her, they've grown all over one rock and several other places. Can they grow to numbers that threaten the tank's overall balance? Anything to be concerned about?