I have never seen anything on how adding CYA effects a pools chemical balance. It is an acid, so how much does it effect PH and ALK? Does anyone have a ratio of what to add per pound for every pound of cynaric acid added? This might be difficult since it takes so long to disolve. I usually add 8 lbs of CYA to SWG new pools over the first week (thats for a pool of about 25,000 gallons). It would be nice to know a set amount of PH or Alk increaser to add with it.

My pH and Alk seem to move hardly at all.

That said, I normally add CYA in the Spring when I'm already adjusting the other parameters so I may not have noticed the CYA affecting anything.

In the following I assume I start with a pH of 7.5 and a TA of 100. 8 pounds of Cyanuric Acid added to 25,000 gallons would increase the CYA by 38 ppm and would lower the pH from 7.5 to 7.07 with no change in TA (the lowering of TA with lower pH is compensated with the addition of TA from CYA itself). To get back to a pH of 7.5, you would add 9.5 pounds of 20 Mule Team Borax with the end result being a TA of 112 ppm. Alternatively, you could add 4.8 pounds of pH Up / Arm & Hammer Super Washing Soda though that would result in a TA of 122 ppm.

Of course, the above assumes no outgassing of carbon dioxide that would raise the pH with no change in TA. So in practice, you may find that the pH doesn't drop quite as much as predicted depending on how quickly the pH tends to rise each day as is typical in SWG pools. Since CYA takes a long time to dissolve, you may find that adding it simply stabilizes the pH during that time when normally the pH would rise. If that is the case and the pH is stable, then the TA will remain 100 but the carbonate alkalinity will decline so to keep that the same you would add (after the CYA is all dissolved) about 4 pounds of Arm & Hammer Baking Soda which would raise the TA to 111 ppm which would give you the same saturation index as where you started (which may or may not be what you want to do).

Richard

excellent reply thank you