What is this on my sand?

[tubz]

My algae on my rocks finally is almost all gone and now my sand is ugly.

 

[jamespias]

How long has this tank been set up? It almost looks like cyano, but a little too early in its development for the bubbles. If it's a new-ish tank it's probably just your next step in your algal succession. Do you have any nassarius snails or anything to help turn your sand?

 

[tubz]

The tank is about a year and a half old. I have maybe 75 or so nass snails

 

[jamespias]

Lastly, are there bubbles in the algae, or have you tested for phosphates? Based on color alone, I would lean on cyano, but there would have to be bubbles. Is this a FOWLR tank? If so, obviously a lights out for two or three days could go a long way.