Diatom help

[TankMan]

I may not be in the correct forum for this, but I need advice. It's been a very long time since I've cycled a new tank as I am now, a 175 gallon, since my 75gal about 8 years ago. My concern is the brown dusting everywhere of diatoms, I presume. There's nothing in the tank now except for the L/R, and the cycle is just finishing, as I tested nitrite today at 0.1, down from 1.0 a few days ago. I filled the tank with ro/di water, a 9 day process right out of my purifier, which tested "green" on the monitor each time I checked over the 9 day period. Are the diatoms caused by the abundance of nutrients present in the water due to the die off of what was once life on the LR? What's next, a WC? TIA, Tim