Are these diatoms?

[Cbryant54]

Hey all, I need help identifying this red/brown covering the sand. Tank is about a year old. It's like it's coating individual sand grains. It does not blow off with a baster, not slimy or stringy. No bubbles. Turned the lights off for two weeks but still there.

 

[Tahoe61]

Have you added new equipment or silicates?

 

[Cbryant54]

Have you added new equipment or silicates?

Nope, nothing new since set up

 

[vlangel]

Hey all, I need help identifying this red/brown covering the sand. Tank is about a year old. It's like it's coating individual sand grains. It does not blow off with a baster, not slimy or stringy. No bubbles. Turned the lights off for two weeks but still there.

Yep, I have it too. I believe it diatomous algae but I am not positive. Its not really on the rockwork, mostly just the sand. As the lights go down, it recedes. I have not tried blackout treatment because it doesn't seem to be hurting anything except that it looks ugly. My tank has a lot of white light because I am keeping ornamental macroalgae and some mangroves along with coral. If you can control the colors of your light and you don't keep macroalgae, you may be able to discourage its growth by increasing the blue and decreasing the white and red since white and red encourage algae growth.