Cya for swg

[Blockparty1]

Good day, I have read through all of the pool school stuff. What I don't understand is the cya vs fc. As I read it it shows that cya protects fc from degrading. However on the cya/Fc chart when you elevate Cya you also elevate FC. I must be missing something. Seems to me like if Cya protects Fc, then you would use lower Fc for higher cya levels and vice versa. Thanks for the on goin education.

 

[mknauss]

A good summary.

CYA Chlorine Relationship - Further Reading

www.troublefreepool.com

For more detail

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

 

[JoyfulNoise]

The misunderstanding comes from the detailed chemistry - CYA has two properties, it protects chlorine from loss by UV light AND it combines with the chlorine to act as a buffer. Free chlorine is a measure of three compounds - hypochlorous acid and hypochlorite ion, which is sanitizing or active chlorine, and chlorine bound to cyanuric acid, which you can think of as chlorine held in reserve. The active chlorine is what does all the work sanitizing and oxidizing while the chlorine that’s bound to CYA is mostly inactive. As the hypochlorous acid and hypochlorite ion get used up, the CYA releases more chlorine. In order to have the proper amounts of active chlorine, the amount of FC must increase as CYA increase. If you keep FC constant but keep increasing CYA, the amount of active chlorine decreases and your water eventually becomes unsanitary because algae and bacteria can grow faster than the active chlorine can kill it.

 

[Blockparty1]

The misunderstanding comes from the detailed chemistry - CYA has two properties, it protects chlorine from loss by UV light AND it combines with the chlorine to act as a buffer. Free chlorine is a measure of three compounds - hypochlorous acid and hypochlorite ion, which is sanitizing or active chlorine, and chlorine bound to cyanuric acid, which you can think of as chlorine held in reserve. The active chlorine is what does all the work sanitizing and oxidizing while the chlorine that’s bound to CYA is mostly inactive. As the hypochlorous acid and hypochlorite ion get used up, the CYA releases more chlorine. In order to have the proper amounts of active chlorine, the amount of FC must increase as CYA increase. If you keep FC constant but keep increasing CYA, the amount of active chlorine decreases and your water eventually becomes unsanitary because algae and bacteria can grow faster than the active chlorine can kill it.

Thank you for that explanation. Very easy to follow. After reading the other linked article I was still a bit confused but now I understand it