What is on my sand?

[KevinJK]

Does anyone know what this purple colored stuff is on my sand?

 

[cloak]

Cyanobacteria most likely.

http://www.reefcleaners.org/nuisance-algae-id-guide

 

[KevinJK]

Thank you.

 

[Ron Reefman]

I've found that more flow will really help keep cyano in check.