Black stuff on zoa frags

[Railrider1920]

Hi folks,
I noticed on a frag of my zoas, there is some black stuff on it. It looks almost like it is painted on. It doesn't wipe off. The stuff is covering the rock, but not on the polyps or the stalk. If I can get a pic after the lights come on I'll post it. Any idea what it is I have?
Thanks,
Rob

 

[twinspots_goby]

it might be some kind of algea. But it's hard to tell without a pic.

 

[Sikryd]

Its probably real dark purple - just algae if it is slippery - could be a small sponge too

 

[EliteReefs]

if you can get a good pick i'm sure one of us will be able to help a bit more. so many things it can be

 

[green machine]

like others have said, its hard to tell with out a picture but I have seen a black sponge going around on frag plugs here and there.

 

[Railrider1920]

Thanks for the replies folks. I cut my finger today and haven't been able to get the camera out yet. When I do I'll post a pic if I can get a decent one.
ROb

 

[zarro]

Black stuf

hard to say with out a pic .But sound like a sponge