any clue what this is?

[Monte]

This thing has been growing on my live rock for a few months now. It started out smaller than pea size and has grown to the size of a marble. It's a dark green to almost black in color.

 

[Monte]

Sorry the the pics didn't go through. I'll try again

 

[steve-s]

Welcome to AquariumAdvice.com

Valonia aka bubble algae. It's a nuisance algae that can spread throughout the tank. If you can remove it without breaking the bubble, you should.

Cheers
Steve

 

[fishfreek]

Bubble Algae. Very carefully remove it with out bursting it.

 

[ReefLady]

Valonia spp., aka "Bubble Algae".