Tested. pH/TA was high. Added acid.
Aaaaaaand.....CYA was freakishly low, somewhere below 70ppm

I'm burning CYA at greater than 5ppm/month....
And before you say "leak", it's not a leak. My CH continues to rise and all other chemical levels (salt) are stable. I think the heat and high UV levels are actually burning it up at a noticeable rate. That, and general measurement uncertainty seems to explain it to my satisfaction.
Plus, I can now make my pool water "primo" because I'm adding -
I have never used this brand before so wish me luck....