Marie,

I agree with you and personally if I had an SWCG I would try to find an optimum "lowest CYA highest FC" combination that I could that wasn't horrible for the life of the SWCG system. Apparently, the salt cell is more efficient at higher CYA of around 60-80 (70-80 is best) for most manufacturers (some say to use a little less) and then the life of the salt cell is based on it's output -- so on longer at higher power degrades the cell faster -- so the life of the cell is dependent on how much chlorine you generate.

Because the loss of chlorine to sunlight is proportional to how much chlorine is in your pool, operating at a higher FC means having the SWCG either on longer or running at higher power or both. At least this is my understanding from others who have an SWCG system. And yes, this is a tradeoff of the "risk" of algae or pathogens vs. salt cell life, though there does seem to be some benefit to the continual dosing and "subset of total water volume" shocking that the SWCG performs so that maybe Ben's chart is too conservative for SWCG systems.

So long as at least 3 ppm of chlorine is maintained, then the pool is at least equivalent to the level of disinfection (650 mV ORP) that is the standard set by WHO and some pool organizations. Wander into this post for more details about ORP and the interesting findings I made from the Oregon Commercial Spas study.

On the other hand, if I had my own SWCG system, I'd probably try to run it at 5 ppm FC (if the CYA were 70-80).

Richard