Bubbly Sludge on GSP

[ccombs]

Sorry if this is too blue, I am color blind so I am not sure if this goop is brown, green, or grey. I just noticed it today after moving this rock of GSP.

It had been doing well awhile back, but it has not liked the new placement for a few months so I tried placing it in a higher flow area. Tonight I noticed this bubbly sludge, thoughts?

Is it part of the sponges?

 

[Afrashz]

Looks like some sort of sponge but I could be wrong

 

[reef lover]

I agree sponge. Manually remove.