Apr 29, 2016
Houston, TX
Pool Size
Liquid Chlorine
Hi all. I have been a paid subscriber to the Pool Math app for a few years now. I've noticed it seems to underestimate the effect of adding dry stabilizer. For all other products such as 10.5% sodium hypochlorite, and 31.45% HCl, the calculations seem pretty accurate, but whenever I add dry stabilizer (Clorox brand, 100% cyanuric acid), the app doesn't get close. For instance, yesterday my CYA was reading about 20. The app said that 10 oz would raise it about 4.5 points for a pool of my volume (17.5k gal). So, I weighed out exactly 10 oz, put it in a sock, and hung it in front of a return jet as per my normal S.O.P. Today, after about 24 hrs of dissolving, I pulled the sock which still had quite a lot of dry stabilizer left, and I tested the CYA. The results showed 30 ppm. That's a 10 ppm increase with far less than 10 oz CYA added. This is not the first time this has occurred. Has anyone else had this issue with the Pool Math app? Is there something I'm not considering or something I'm doing wrong that would make my CYA rise far more than expected from adding the recommended CYA amount?


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

When I add CYA it takes a few days for my readings to stabilize. (No pun intended.) :mrgreen:

If I take a reading after only 24 hours, it is almost always too low, but if I wait another day or two it will increase.

And as Sunny points out above, the test is a lot subjective.


Jim R.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
The CYA test is, at best, +/-15ppm in its reading assuming you are very careful and do three or four readings. There’s no way you can accurately measure a 4.5ppm increase, it’s in the noise.
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