CYA/FC Relationship during SLAM

[FloridaPoolNewbie]

I'm curious to know why a lower CYA calls for lower FC during SLAM. I just naturally thought a higher CYA would be more efficient and call for less FC.

I also wonder why a lower CYA (let's say 30 in this example) calls for 12 ppm FC, as I would assume higher FC would be better at clearing a pool up. Thanks for answering my random thought lol.

 

[JoyfulNoise]

The “shock” level of chlorine for a pool is for the FC to be 40% of CYA. That is MORE THAN ENOUGH active chlorine (hypochlorous acid and hypochlorite) to kill pathogens and oxidize waste. Anything more than that would be a waste of chlorine because, as the chlorine concentration increases, so does it’s loss to UV photolysis and self-extinction. Essentially, 40% is a good working value that creates the right balance of clearing versus chlorine loss.

Also, if the chlorine concentration is too high, you risk damaging equipment and bleaching surfaces.

 

[PoolStored]

Here is a good read if you are into the deeper end of the "why?".

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

 

[Mdragger88]

In short the more cya you have the more of your chlorine is “bound” & unavailable for sanitation. The higher cya doesn’t make fc more effective it only provides it more protection from the sun.

CYA Chlorine Relationship - Further Reading

www.troublefreepool.com