Wow...I'm so glad to read this thread. I've pretty new to the hobby and just noticed sponges popping up in about five different places in our 100 gallon tank. I wasn't sure if I needed to worry about it or not.

You guys keep referring to "as long as it's not getting close to the corals" so I have to ask: is it a problem that one of mine is coming up right next to a little mushroom, is actually touching the mushroom? Should I pull it off the rock to allow the little mushroom to grow?

Thanks,
Kristy