Does CYA have a shelf life?

[newpoolguyinmo]

Hi All,

I recently replaced some water through backwashing, too much rain, etc. My CYA went from 50 to 30 so I wanted to get it back around 40. The pool calculator says for 16,100 gal I needed 22 oz by volume of stabilizer to go from 30 to 40. I got the stabilizer (100% cyanatic acid) at Lowes and added 22 oz in a sock in front of the skimmer. Waited a week, and it still tested at 30, no increase at all. I then added 45 oz by same method shooting for 50 this time and waited another week. The last reading was barely over 40. So, it took 67 oz to get from 30 to 40. Could the CYA I bought be old and weak?

Here are my latest test results.

FC 5.0
CC 0.0
TC 5.0
pH 7.6
TA 100
CH 210
CYA ~42
Water temp 75 deg.

Repeated CYA test 5 times with same results.

 

[JasonLion]

CYA doesn't go bad if it is kept in a closed dry container. There are a few places that sell 50% CYA, instead of 100%. Check the label on you package. It is also possible that it is working normally, but the CYA test simply isn't precise enough to tell you what is really happening. The CYA test is +-15 at the best of times.