From the article recommended above by fishwrangler:
"Brown Algae (diatoms) are more likely to appear in low-light aquariums and new setups, where nitrogen (N) is low and phosphate (P) level is high, with excess silicate (SiO2)."
Thank you, fish wrangler! I'll google how to raise nitrogen and lower phosphate - or at least not set up such a situation again, if possible.
I just finished scrubbing the visible diatoms off the rocks in old tank water and wiping the tank walls, although those appeared clear. When I added the water back in I let it go much higher to the top of the tank as it was suggested somewhere to me, (can't find it or remember which thread!! So sorry, brilliant and wonderful AA Forum member.)
Tank top now:
While doing a 75% PWC, I WAS finally able to locate all three of my Nerite snails. I had only been seeing one at a time and was worried it was the same one and that the other two were dead and decaying under somewhere. (A little dramatic, I know.)
~ Sent with the velocity of a European laden swallow