Is this a diatom bloom?

[RedhawkReefer93]

 

[sricorals]

yes.

 

[vertigo01]

My diatoms never looked like that.
They made the sand and rock look as if it were covered by brown dust.
That looks sort of like Cyano. Although I could be wrong.

How long has the tank been cycled?
Water parameters?

 

[SDReefer]

Yeah diatoms are usually brown. Looks like cyano. How old is your tank and how much flow do you have? If it's a relatively new tank, cyano is a part of the tank establishment process.