Is this purple stuff good or bad?

[cmonicarl]

This has been growing on my rocks for a while now. Some of it seems like soft and some is like in the rock.

 

[willbratz]

Cyano bacteria not good.

 

[54seaweed]

agree with Will on soft stuff
but the hard stuff looks like Coraline thats good I'd kill for big patches like that on my rock