Opening pool, CYA unexpectedly low? Do reagents go bad over winter?


New member
Jun 20, 2019
Northern Indiana
We purchased a new home with a pool last summer. We are first time pool owners. The previous owner used puck chlorine tablets (left a couple large tubs full), but when I purchased the testing kit the CYA was super high, like off the meter, estimated ~300. After a few significant water exchanges we had it down to 58 and proceeded from there using liquid chlorine instead. I was expecting to lower it a bit further when partially draining for winter and replacing this spring. However, when opening now and adding water (~15% replacement), the CYA levels measure below 30 (dot still visible when the tube was full).

Other numbers were roughly where I expected based on last year numbers except for chlorine which had essentially disappeared over winter. FC/CC at 0 (at SLAM at time of closing), PH at 7.8 (maybe slightly lower), TA 180, CH 260.

The reagents were stored inside in a cool, dark, climate controlled location. Is it possible for the reagent to go bad (shows a Sept 2020 date on the bottles)? Is there anything that would otherwise cause the CYA to drop from last fall to this spring, I thought only water exchange would do that and the amount of water I replaced should have been far less than enough to drop it more than in half?

I'm a newbie, so thanks for any assistance.
Last edited:


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Welcome to the forum!
Your test reagents should be fine. The R0013 for CYA is very stable.
The CYA does degrade some and you lost some due to water drain before winter. I would only put in 20 ppm worth to start and then retest.
I suggest you read ABC's of Pool Water Chemistry.


TFP Expert
LifeTime Supporter
Jul 21, 2011
Eastern Ohio
Pool Size
Liquid Chlorine
I almost never keep any CYA in the water over the winter. It’s no worries, just slowly raise it and you’ll be fine. Just make sure to allow the water to warm up a bit right now when testing as the CYA test does slightly vary depending on the water temp.
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