Diatom bloom? Brown stuff on rocks...

[i_declare_bankruptcy]

I want to make sure I know what is growing on my rocks! It's kinda hard to query for algae; googling "brown stuff growing on rocks" doesn't exactly yield specific results haha. Anyways I'm pretty certain these are diatoms and a normal issue for my ~2 month old tank to be facing but I just want to double check and see what everyone thinks. My Nitrates are around 1-2ppm and my Phosphates about 0.01. TDS of my RODI water is typically 0 but last couple top off fills were TDS 2 and 4, respectively. I don't think I've noticed an increase due to TDS increase but I'm replacing the unit regardless (they had bad tech support, buying a BRS unit now).

If you have any tips for dealing with it let me know -- should I just let it do its thing? It's spreading slowly but I'm noticing more and more each day. Haven't noticed anything on the sand but my CUC is pretty exceptional!

20181020_101429 by Andrew English, on Flickr

20181020_101440 by Andrew English, on Flickr

 

[PDR]

I'm not great with algae ID, but I don't think those are diatoms. I have something similar that has been growing on my back glass for quite some time. Have you tried blowing it off the rock?