Help to ID.

[KeenHGoD]

My tank is about 4 months old ( 32g Biocube). I have 2 clownfish, 3 Mexican turbo snails, 2 larger zombie snails, 4 small ones, 3 blue legged hermits, Duncan coral, 3 zoanthids, 1 waving hands. Green star polyp. Some coralline algae growing on back wall, and intake vent.

I’m new btw first saltwater tanks. Now the iD I was needing…. It looks like black exhaust soot. Been on one rock for a few weeks now.

Thanks in advance! Btw love all the knowledge here it’s overwhelming.

 

[ISpeakForTheSeas]

Welcome to Reef2Reef!

My first thought would be a sponge, but could you get some pics of it under white light?