Anyone ID this brown stuff on sand?

[Reef.]

Anyone know what this is, just turned up when I reduced the flow from my powerheads.

 

[T-J]

Guessing it's a new tank. Most likely diatoms.
Worst case scenario: dinos.
Is it "dusty", or look like "snot" with bubbles.
Dusty - diatoms
Snot - dinos

 

[Reef.]

Guessing it's a new tank. Most likely diatoms.
Worst case scenario: dinos.
Is it "dusty", or look like "snot" with bubbles.
Dusty - diatoms
Snot - dinos

No tanks been up for over a year, they literally turned up the same time I reduced the flow, sand was white previously, po3 is .04 and nitrates under 15.

It disappears as soon as I turkey based it, stays away until lights come on the next day.