Quote Originally Posted by chem geek
Absolutely no offense taken at all. You are correct that I have zero experience with SWG systems, I agree completely with your points, and I'm the one who has to be careful not to offend. My educated guess as to what is going on is not inconsistent with the real-world results and yes, it's the theory that must match the real world, not the other way around. I was just dumbfounded with the initial claim that the salt cell has superchlorinated levels of chlorine AND that this was getting applied to all of the pool water (in a reasonable time).
You are right that it is only being applied to a fraction of the pool water but it is an ongoing process and I would believe the effect would become cumulative after a while...in much the same way UV sterilization would only kill the bacteria in the reaction tube but with each pass there would be less and less bacteria in the whole of the water. I know that UV light has to be in close proximity to the water for sterilization to occur from my experience with it in aquarium use and not all the water flowing through the tube receives enought intensity to completely kill the pathogens present. Ozone, also only works on the water in the reaction chamber. In fact, no residual ozone is supposed to be in the water when it enters the pool. Once again the benifit seems to be gained from an incremental effect. Plus ozone acutally depletes chlorine levels somewhat so a negative factor is introduced.
There is one big difference between UV and ozone sanitizers vs. SWG as far as I understand them and that is that the former do in fact "do their work" on the entire volume of water that flows through their chambers so that after a few hours with one turnover of pool water, the majority (I forget the number and how to calculate it, but I think it's around 70%) of the water in the pool has been sterilized and oxidized at least once. This does not appear to be the case with the SWG and instead some fraction of the water goes through amounts of superchlorination. I could be dead-wrong about how the UV and ozone systems work so if anyone knows if they "slow down" some part of the water in their systems in order to more effectively disinfect and oxidize, please let us know.

Since putting in liquid chlorine (bleach) also superchlorinates a part of the pool water when it is introduced into the pool, then the incremental benefit of the SWG probably derives from its continual dosing which is more optimal. I wonder if people without SWG were to manually dose their pools more frequently (with smaller amounts of chlorine each time) and did so over pool jets at both ends of the pool if they, too, could operate at lower levels of chlorine safely.
It would seem that systems that use ORP controllers and peristaltic pumps would achieve this but I don't believe that optimin ORP mv levels are reached with lower chlorine concentrations. And it is a well known fact that CYA disturbs ORP readings. Whether these actually have an effect on the actual sanitation I do not know. I would be intersting to compare pools with SWGs and peristaltic pumps at comparable FC levels and CYA levels and see if, in actual use, similar results would be obtained.
My guess is that they could, but I have no idea what the required FC level would be between "once a day" well-distributed manual dosing vs. the continual dosing of the SWG.

The 3 ppm FC level that you found to be required for your pool is still very safe from a disinfection point of view since 70 ppm CYA, 7.6 pH and 3 ppm FC gives 0.017 ppm HOCl which is above the 0.011 "minimum" that appears to be needed for disinfection (and that's in non-SWG pools and spas).

Again, I think SWG is great and just because I "bash" a specific claim doesn't mean I think the technology as a whole has no net benefit. On the contrary, I regret not having one installed when we put in our pool (it was not mentioned as an option by our pool contractor and I knew even less about pools then than I do now).
A most interesting discourse!