these threads might help http://www.3reef.com/forums/id/some-type-sponge-71677.html and then this one a few weeks later http://www.3reef.com/forums/inverts/under-attack-need-advise-72729.html at the end of that last thread, a 3 hour soak in RO water followed by a good scrubbing followed by a good RO rinse... to follow up, the sponge came back. That rock is now going through a complete nuking process. Beneficial? Sure. But dang unsightly and from the looks of this beast I would not have been surprised if it overtook my coral. The purple tip hammer frag... I got that off eBay. It's also where the sponge came from. I'm not buying off eBay anymore.