Ineffective granulated CYA?

[jmastron]

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.

 

[woodyp]

If that stuff was sealed, never got wet, it should be as god as day one.

 

[zea3]

The CYA test is rather subjective to read and is accurate +/- 10ppm and you only added enough to raise the CYA by 10ppm. You would have to read the test under the same conditions as the original test to get a comparable reading. With a CYA addition this small it will be difficult to measure with that much precision. Had you added 4lbs and seen no difference I would be more concerned. Go ahead and add the other 2lbs and try and keep the test conditions identical (same time of day, same type and amount of light) as much as possible. You can also pour the test solution back into the mixing bottle and read the test a couple more times and use an average of the tests for the result.

 

[themitzelfamily]

We are still working through balancing our full sun CYA/chlorine levels ourselves but some of the best advice we got was to always do the CYA test holding the view tube at your waist with the sun to your back (so tube is well lit but in the shade). Do the test and record your result, then pour it back innthe mixing bottle and use the same test liquid to repeat a couple more times and use the average as your estimated CYA level. Like zea3 said above. Good luck!