I have some strange black looking spots on the bottom of my pool that did not vacuum up. I was able to scrape a few off with my fingernail, and I could see that the little bit around and under my fingernail was actually dark green, not black. But my pool water itself is very clear, even sparkling. If this is algae, it's just in little colonies on the bottom and none floating in the water. I don't seem to have had any strange amount of chlorine loss.
I haven't done a full set of readings yet to see if I have any CC.
CYA = 55 (about 1 wk ago)