Black substance on Live rock?

[KSum89]

Its not really a oil spill but it kind of looks like it.. Someone help me figure out what it is please.

 

[Bige]

sponge. Looks like sponge, maybe. Its not algae is it? Is it new rock or has it been in a while?

 

[KSum89]

Its been on the rock for awhile.. I purchased it with it on there. Straight from the sea to my lfs to my aquarium

 

[thincat]

As Bige stated it's more then likely a sponge.

 

[KSum89]

As Bige stated it's more then likely a sponge.

Good or bad thing?

 

[thincat]

Most sponges are just fine. Just keep an eye on it so it don't over grow something that you like.