ID this stuff please

[Mik_101]

Dose look like a sponge of some sort. Was it a hitchhicker?

[Renegade]

the fact its growing on the underside and hes concerned to know what it is, makes me think he didn't buy it but thats my opinion.

[Snappy]

Sponge------ I have them in red, orange, purple, green, black & white.
Good filters. There are far worse hitch hikers you can get.

[Der_Iron_Chef]

Definitely true, Greg! But here's a question: has anyone had a sponge overgrow corals? Are they dangerous in that sense? And if so, how do you trim them back/keep them in check?

[Snappy]

Originally Posted by Der_Iron_Chef

Definitely true, Greg! But here's a question: has anyone had a sponge overgrow corals? Are they dangerous in that sense? And if so, how do you trim them back/keep them in check?

Sponges that encrust the rock IME generally grow in low light areas so they don't compete with the coral. Also the corals give off toxins to ward off intruding species. I have had sponges grow beside a coral but never compete for the same space. Some sponges have long thin stringy branches that don't look very nice so those I have just pulled off or cut with scissors.