On my zoa

[Mikek]

So to you once again my esteemed, knowledgeable, fellow aquarists, I ask, should I be concerned about this brown stuff on my giant zoanthid and/or the hairy/grassy stuff hiding underneath (which I only just noticed after taking this pic). The zoa seems healthy enough, but I want to be pro-active if necessary.

As always, thanks for your time and knowledge... :)

 

[ErinCahir]

It kind of looks like sponge. Is it squishy?

 

[Mikek]

Seems to be, but not very thick, and not covering much of an area, so tough to tell for sure. Am I correct in assuming sponges are safe filters? Or do they attack coral?