Black stuff on live rock???

[Westbery]

I set up my tank approx 3 weeks ago. Recently I rearranged the rocks and I realized that the rock on the far left of the tank is growing this black stuff with air bubbles under it. Any idea what it is? Should I just wash the rock with fresh salt water?

[Salamander]

Not the greatest pics...but I think its cyanobacteria. There are plenty of threads on here to read about it.