Thank you for the responses!
I put 1 gal Home Depot (10%) chlorine in on Friday, and today the numbers are:
I'm using the TF-100 cloudy tube test, and there's 0 cloudiness (maybe my chemicals are old?)
I should try disabling the auto-filler.
1 gal in 36k should be about 3 ppm. And most will lose 2-4 ppm a day. 3 days later it’s surprising you had any left. So there is that issue.
The CYA of course needs to be raised as it may have slowly dropped and you’re just seeing it now. 30 looks good……. 20 looks like something at least and under 20 is almost impossible to notice anything at all. Could be simple, might be ammonia.
I believe that was what @Donldson was referring to because if you have a CYA of zero and the FC gets eaten almost immediately, then it’s an ammonia problem. So add 8 or so FC (2.5 gals ? Whatevs poolmath says) and check it 30 mins later to see if it held. If it does you just need CYA and daily doses of FC.
To close the loop here: After cleaning out the incredibly dirty cartridge filters, bringing the CYA up to ~35 (and +2 gal Cl & 1 gal muriatic), and buying a new Kreepy Krauley, the water tastes great again & sparkles! Just in time for cold weather to roll in here in San Jose