What is this algae bloom?

[SaltyPirate]

This is my second tank and it’s currently cycling, the cycle has only been running for a week.
This black “algae” appeared when the tank was being filled with RODI water, I had to fill it over the course of three days.
What is this algae?? It’s only in the areas that have high flow. Lights on only to show the algae

 

[Zach B]

I believe that’s cyano, a little hard to tell

 

[vetteguy53081]

Photos are black and white but looks like diatoms

 

[SaltyPirate]

Photos are black and white but looks like diatoms

Photos are in colour. It’s a light dusting but it’s black and started appearing when it was only RODI in the tank and has stayed since I’ve added salt and started the cycle.

 

[Garf]

Photos are in colour. It’s a light dusting but it’s black and started appearing when it was only RODI in the tank and has stayed since I’ve added salt and started the cycle.

I would try siphoning it out, what ever it is. Black is an odd colour to have, but presumably it’s a contaminant from the sand.