I want to mark this thread as I'm having a similar issue. I've been trying to get my levels corrected over the past week so I can fire up my newly installed SWG. I added 4lbs of granular stabilizer (HTH walmart) last week expected CYA number to jump to 30-40. I tested when I got back this week (work out of state during the week) and nothing.
I don't want to hijack your thread, I just feel like we are in the same boat. I have no idea where all the CYA went and why 4lbs didn't move it. We've dumped about 1500oz of chlorox bleach along with 3lbs of Cal Hypo Super Shock over the past 2 weeks. The water is crystal clear, but sometimes there is what appears to be dead mustard algae on the bottom. (Hence the constant shocking.) I'm not home enough to properly do it as I've read on the forums. I have to resort to lots of chlorine and hope it survives the week.
I hope we can figure out our CYA issue. There isn't a possibility of getting a false negative is there?
My numbers from Taylor Test Kit read:
CYA: 0-20 (can see dot at full but some cloudiness)