Identify?

[blackstrat77]

Hi all! Can someone please tell me what these are? Nitrates are around 20 ppm and I don’t have a phosphate checker. There are 4 spots of these on the rocks. Nothing on the sand. It does not go away when lights are out. I am praying its just diatoms.

 

[P-Dub]

Hi all! Can someone please tell me what these are? Nitrates are around 20 ppm and I don’t have a phosphate checker. There are 4 spots of these on the rocks. Nothing on the sand. It does not go away when lights are out. I am praying its just diatoms.

Can you easily blow it off? If so, likely diatoms. If not, likely algae.

 

[neo1738]

Looks like diatoms.

 

[Reefer Matt Verified Media Partner]

How old is the tank? Could be diatoms or cyano.