I recently decided to increase my CYA from ~35-40ppm to the 50-60 range, because with our always sunny, often hot days, my daily FC loss is a bit higher than I'd like; last year when we bought the house the 80ppm CYA worked better. I understand the tradeoff of higher required SLAM levels, thus decided on 60 as a reasonable compromise level.
Anyway, I had some unopened HDX granulated stabilizer from last summer, listed as 99.0% Cyanuric Acid. I put 2 pounds in an athletic sock last Wednesday, hung it from a stick near the return, and it was all gone by the next night. I waited a full week (until last night) to test again; result: 35-40ppm, same as before. I have the 50ppm standard solution, and verified again, so I'm pretty sure I'm doing the test right. The weather has been cooler, thus the cover on more, so it's been harder to see if FC usage is down.
Does it ever take longer than a week to register? Can the CYA either be or go bad to the point that it adds basically nothing? I had only added enough to get halfway to the goal, so I can try another 2 pounds of another brand and even if the first magically appears later it won't be a problem.