Help with algae

[Aaron Stillwell]

Does anyone know what this is?

 

 

Sent from my iPhone using Tapatalk

[gws3]

Cyanobacteria. Siphon it out the best you can. Then use a powerhead to blow off the detritus on the rock. Bump up flow in that area slightly. See if it comes back before doing anything else. Patches like this are often caused by an area where detritus has settled and the flow is weak.