Need help IDing

[CamGG]

I can't tell what this is. It's very brown in color. It looks lighter at night but doesn't entirely disappear. It appears to be getting worse now that I've discontinued my GFO. What's weird is it won't touch one side of the tank.

Phosphates are 0.05-0.08
Nitrates are ~15

 

[vetteguy53081]

Pics are too blue to confirm but appears as cyano
Assure your nitrate and phosphate levels are not elevated