Weird Algea/Cyano?

[ReeferDan22]

Hey Guys, I need help identifying and treating this algae in my tank. Chemi clean seems to do a bit to it but it is very persistent and form a mat that bonds to the sand making it hard to vacuum up.

No bubbles, almost black. Parameters are all within a good range. Nitrates are 7 phos is around .02.

Please help me figure this out!

 

[ShakeyGizzard]

I have had a black looking algae show up in small spots on a crab tank I have. But they went away with just usual maint. and was never on the sand