I've been a lurker here for a year or so. I switched to TFPC/BBB late in the season last year after struggling with my pool all year. I purchased a Taylor K-2006 and found my CYA last year to be 200 or more. I did a series of partial water changes on my 20000 gal vinyl pool with city water and got it down to 100. I covered the pool over the winter and opened it up a few days ago. The water temp was already to 70 here in SC and there was some blue-green algae color, but not severe (the cover has a few holes in it). My numbers aren't all that bad:
The mystery is the low CYA. I dropped the level by 5000 gallons during the close, if that, and just refilled. I was expecting a number closer to 75. I know these things can't be predicted exactly, but considering how hard it was to drop the CYA last year, I'm curious where that substantial delta could have magically gone. 40 isn't a bad number, much better than a high number, but my pool gets a lot of direct sunlight so it may be on the low side now.