Black or dark green algae growing on chaeto

[branortanava]

I've got a decent size ball of tumbling chaeto in a refugium, but I've noticed over the past few weeks that it's got a black or dark green algae growing on top of it. That algae grows on the side of the chaeto that faces the light, and it's more dense toward the center. Would it be cyano? Anything else?

 

[shwareefer]

Likely a green slime algae from high nutrients. I would remove it (outside of the tank), even cut the affected parts of the chaeto off.