Thanks for the help, chem geek.
I brought it up to about 25 ppm last night (~9pm) - I overshot :-(
At 7am it was 15 ppm FC, no CC that I could read.
9am : 13 ppm FC
1:30pm : 2 ppm FC

I've tested again and see basically no CYA in my test.

I took a water sample to the pool store about 2pm. They concur with 0.6 ppm FC, CYA of 32 ppm. The pool store, of course, wanted to sell me phosphate remover (they tested at 500 ppb phosphates), which I declined.

According to the "Best Guess Guide", the behavior I see is more like the "nearly zero" CYA than the pool store's report of 32 ppm. 32 ppm feels like a reasonable target for CYA...

I did buy 1.75 lbs of CYA. According to the label, 1.75 lbs of CYA should raise the level in my 20K gal pool by about 10 ppm. I went ahead and added the 1.75 lb, plus more bleach to keep FC above zero.

So, questions:
1) I assume I did good by ignoring the phosphate remover, right?

2) Since I read basically zero CYA and the pool store reads 32 ppm, adding just one container (1.75 lb) CYA seems warranted and safe. Was that reasonable, or should I add more (or, maybe, less)?
2a) Is there a consensus on a good target for CYA? This is an outside pool, with moderate/low sun exposure.

3) Chem Geek mentions that this can happen to a pool that is "let go with no chlorine over the winter". I honestly don't know how to maintain chlorine levels over the winter... I start adding a little chlorine early in the spring, then open the pool later (about now). It is always green, sometimes I can't see the drain at the deep end. I vacuum, adjust pH, then start adding bleach, vacuum, repeat..., until it clears up (usually 2-4 days). Am I doing this in a reasonable fashion?