what is this

[mrdebit1]

I have some of this black stuff that grows on my rocks and when i flake it away it is gray underneath. if i touch it kindda feels spongy i am pretty sure it would be some kind of algea but i cant find anything that will eat it. when i flake it away it just beaks apart and some of it attaches to other rocks and starts to grow. I have checked my water and find nother to much out fo the norm.

 

[jamos6]

A picture would be nice but it might be some type of sponge.

 

[deejeff442]

i have a big rock with alot of the black sponge .
i like it .
its grows pretty slow and hasnt spread to any other rocks yet.