I just finished a total drain and refill here in Phoenix. After a week I have everything balanced out, the CYA up to 50, pH is 7.6, and water is crystal clear. However, when the pool was totally empty and dry, I washed down the walls of the left over "dust" that I was having a hard time vacuuming/brushing out of the pool previous. I was convinced I had a lot of desert dust settled in my pool the last few months, but now I'm thinking it might have been yellow algae. When it was dried out and swept up into a pile in the bottom of the pool, it looked like a light brown and VERY fine powder, almost talcum powder in consistency. Since it was hard to brush up and vacuum (it tended to stick to the PebbleTec), I'm now thinking it may have been yellow algae instead of dust.
Thoughts? I wish I had kept a sample. Maybe it could be tested somehow.