What the heck is this?!? There also seems to be more of it spreading along the LR. It's growing on top of some bubble algae, and coating a part of a xenia. Doesn't look good....
I don't know if this is the same stuff...it's the same color, but without the siphon--or whatever that is. It's attached itself to an already sick piece of xenia, and is covering the LR.
Interesting. I have the same stuff in my tanks growing in shady spots out of the light. I've never seen it attatch to a coral though. Maybe someone else will know. Try a post with whats growing on my xenia as the name. Sometimes various types of inverts will grow symbiotically with a coral or make a coral their home.