How did you test salt? That seems like a drastic swing in the matter of a few days. If you're reading this off the SWG, I'd recommend getting a proper test for the salt - https://www.amazon.com/TAYLOR-TECHNOLOGIES-INC-K-1766-CHLORIDE/dp/B001DO35EU

CYA doesn't change much. I usually test at the beginning of the season and that's it. Unless you have a lot of splash out or have to drop water level, I wouldn't go crazy testing this. Though do round-up - if testing at 37, make it 40.

Highly recommend TFTestkits for any kits/reagents. They're tied in with TFP - good people.

Here's the stabilizer I use - https://www.amazon.com/gp/product/B00PZZF9P6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Believe some Lowes also carry this or similar.