- Aug 6, 2019
- 173
- Pool Size
- 1
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
According to the simplified Chlorine/CYA chart, the target FC for a SWG pool with 70ppm CYA is 5ppm.
But according to the Pool Water Chemistry thread, the minimum recommended level of HOCL (disinfecting chlorine) required to kill both bacteria and algae is 0.05ppm. The rough formula to calculate HOCl (assuming the CYA:FC ratio is high enough) is:
(HOCl as ppm Cl2) = (FC as ppm Cl2) / ( 2.7*(ppm CYA) - 4.9*(FC as ppm Cl2) + 5 )
Plugging in 70ppm CYA and 5ppm FC, this works out to:
HOCl = 5 / (2.7*70 - 4.9*5 + 5)
= 5 / (189 - 24.5 + 5)
= 0.03
Thus, it seems that a target FC level of 5ppm at 70ppm CYA is too low? Richard Falk's (chem_geek's) detailed Chlorine/CYA chart recommends a target of 8ppm FC at 70ppm CYA, with 5ppm being the minimum.
Granted, I haven't read through the entire latter thread, and I had to struggle to make it through the "Pool Water Chemistry" thread. Please let me know if I'm missing something. Otherwise, it seems that perhaps the simplified Chlorine/CYA chart in the first link above should be updated to reflect the target values in Richard's more detailed chart.
But according to the Pool Water Chemistry thread, the minimum recommended level of HOCL (disinfecting chlorine) required to kill both bacteria and algae is 0.05ppm. The rough formula to calculate HOCl (assuming the CYA:FC ratio is high enough) is:
(HOCl as ppm Cl2) = (FC as ppm Cl2) / ( 2.7*(ppm CYA) - 4.9*(FC as ppm Cl2) + 5 )
Plugging in 70ppm CYA and 5ppm FC, this works out to:
HOCl = 5 / (2.7*70 - 4.9*5 + 5)
= 5 / (189 - 24.5 + 5)
= 0.03
Thus, it seems that a target FC level of 5ppm at 70ppm CYA is too low? Richard Falk's (chem_geek's) detailed Chlorine/CYA chart recommends a target of 8ppm FC at 70ppm CYA, with 5ppm being the minimum.
Granted, I haven't read through the entire latter thread, and I had to struggle to make it through the "Pool Water Chemistry" thread. Please let me know if I'm missing something. Otherwise, it seems that perhaps the simplified Chlorine/CYA chart in the first link above should be updated to reflect the target values in Richard's more detailed chart.
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