unable to maintain chlorine levels

[PoolDoc]

Thanks for the page numbers -- I've printed that out, and will look at them.

. . . Now. Ignore all that stuff that I asked about; those are useless metrics.

I’m still experiencing small algae recurrences.

Questions, if I may:

1. Which recommended guidelines is best to use, APSP or NSP, for my situation?

Neither. Both include unnecessary calcium recommendations, and do not adjust chlorine levels for CYA level. (Do you mean NSPF?)

2. Which guideline should be use for total alkalinity, given a salt system… 80 to 100 or 100-120 ppm?

Lower levels are less likely to scale.

3. Please explain PHMB (listed on the guidelines) versus pH? The kit doesn’t test for PHMB. Should I bother with it?

It's Baquacil. Ignore it. Had nothing to do with you.

4. How do I use the CYA Stabilization number? What is the min, ideal, max scale.

Ignore it. Read the Best Guess page, linked in my signature.

5. Ditto the Saturation Index?

Ignore it.

6. My 80° water temp is unusually low now due to record low temps and rain this summer. Usually struggle to keep it below 90°. What is most important criteria to watch for when water temp is that high?

Maintaining appropriate (Best Guess) chlorine levels.

7. I’ve always been told Calcium should be zero or as low as possible in vinyl lined pools. True or not?

Not true. On a vinyl pool you don't need to ADD calcium but you don't automatically have to lower it, either.