Coralline or Cyno

[dlh]

I can't tell. It's been on this rock for 3 weeks, nothing like it anywhere else in the tank.

 

[Soren]

Most likely cyanobacteria, but you can tell based on how fast it grows or how easy it is to clean off the rock.
Coralline algae grows slowly and is quite hard to clean off.
Cyanobacteria grows/spreads quickly and blows off rocks easily.

 

[dlh]

Most likely cyanobacteria, but you can tell based on how fast it grows or how easy it is to clean off the rock.
Coralline algae grows slowly and is quite hard to clean off.
Cyanobacteria grows/spreads quickly and blows off rocks easily.

 

[dlh]

Well darn you were right! Blew off easily