CYA for Salt Chlorinator Pools II

[chem geek]

Richard,
I don't mean to offend you
Perhaps SWGs need to be looked at in the light of this as having 2 separate functions: To generate a residual FC level for the pool and to superchlorinate a small quantity of water in the reaction cell during cell operation to constantly destroy free floating algae and oxidize any nitrogenous compounds in much the same way an ozonator would.
It is a given that theory often does not hold up in field condtions because of other factors that are not taken into account.
Your thoughts on these points would be appreciated.

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).

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. 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).

[waterbear]

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!

[Poolsean]

Richard, no offense taken in any of the responses here. What's interesting is that scientific calculations "should" prove to be consistent with lab conditions, and I'm sure it does. However, real world applications show differently, mainly due to (IMHO) external parameters that are too diverse to pinpoint.

My unscientific mind says that what I see in real life, is what I can report on. Just like Ben's best guess charts are based on his many years of actual experience and research and have proven highly effective. The longevity and membership here, proves that point. Who would have ever thought to grab the gallon of bleach and box of 20 mule team from the laundry room to take care of a pool?!
Ben's wife must have absolutely killed him the first time she saw him sneaking off with the bottle of Chlorox!

You chemistry GEEKS, sorry Chemgeek for borrowing on your name, absolutely are amazing with your knowledge. I have a hard enough time converting Celsius to Fahrenheit! I cheat and just double ( I THINK it's suppose to be times 9/5, rather than times 2) the Celsius and add 32.
I have to admit though, I am learning quite a bit from this string.

Thanks y'all

[chem geek]

Well, we got moved to The China Shop (thank you Ben, if you're the one who did it) and this is appropriate for where this discussion has moved. It's not really about advice on problems or answering questions on CYA for SWG systems anymore since most everyone is in agreement that with current salt cells the CYA should be kept at the manufacturer's recommended higher level (70-80) to improve efficiency of the cell. And I think it's pretty clear from the real-world experience that SWG pools generally have no CC and fewer algae problems (with a few exceptions) on average than manually dosed pools. The issue is why this is the case and it's not clear to me that it's the chemical process in the salt cell that is the source of these benefits or if it's the constant and automatic maintenance of chlorine levels or the continual dosing and at least partial superchlorination or what.

I absolutely agree with you and appreciate the real-world experience and feedback and also know that it won't always match a scientific model. The main reason I like to have a scientific model or at least a partial understanding of the real-world isn't just a curiosity, but also to be practical to be able to predict and potentially to be more accurate. However, if a good model that reasonably fits the real-world data and predicts accurately is not found, then I'm fine with using the "gut-feel" tables based on experience. After all, the chemical and biological model for how asprin works was only recently discovered, yet asprin was (and still is) a very valuable drug for over a hundred years (for the synthetic -- willow bark was used long before that).

There's also another more personal reason that I got "plugged in" to the superchlorination debate in SWGs and that is that I had just come back from the off-site library storage facility in Richmond where I looked up the original O'Brien article on "Equilibria in Aqueous Solutions of Chlorinated Isocyanurate" that was presented at the "Chemistry of Water Supply, Treatment and Distribution" symposium in 1973 and published in 1974. In his paper, he explicitly states the problem of using too much CYA in pools because of how much it ties up the chlorine leaving very little disinfecting chlorine left. He recommended CYA concentrations on the order of 25 ppm. His paper is the de facto industry standard for the equilibrium constants that control the chlorine CYA relationship. So I was upset at how an entire industry of CYA manufacturers would (probably intentionally) ignore this data and promote Tri-Chlor (and Di-Chlor) without limitation until rather recently. It's kind of like the tobacco industry ignoring their own results on the health hazards of smoking. Well, OK, a greater likelihood of developing algae in a pool isn't the same as the risk of getting lung cancer, but you know what I mean. I was upset, nevertheless, and let this emotion spill a little into the superchlorination discussion.

Richard

[aquarium]

So, the entire residential pool chemical industry has organized itself for intentional failure since 1974? Why haven't there been huge class action lawsuits against the obvious deep pockets, like, oh say, DuPont?

[chem geek]

So, the entire residential pool chemical industry has organized itself for intentional failure since 1974? Why haven't there been huge class action lawsuits against the obvious deep pockets, like, oh say, DuPont?

I was partly being facetious when I said the CYA manufacturers "intentionally" ignored these results. I have no evidence that they saw these results back when it was discovered though I do know that at least one company (whom I've had contact with) knew about it since 2004 (see pages 15-17 of EPA Document). I do not want to cast dispersions on these companies. The guy I communicated with was fairly forthcoming and we did not discuss the historical promotion of CYA products -- I was mostly just trying to solidify the technical data through alternative sources.

Nevertheless, it doesn't take a whole lot of imagination to see that companies that make a product whose excessive use can lead to problems would not be the first ones to say "limit your use of our product", especially since this mostly just leads to people buying highly profitable specialty products (algaecide, non-chlorine shock, etc.) to fix the resultant pool problems. Technically, you could just keep ramping up your (FC) chlorine levels to higher and higher amounts to still reamin "safe", though you would be losing an awful lot of chlorine doing so (since even the chlorine tied up in CYA degrades in sunlight, albeit more slowly with a half-life in direct intense sunlight of around 8 hours).

I don't want to start a crusade on this issue, especially since it seems that the manufacturers are now starting to disseminate the advice of keeping CYA levels in check.

Richard

[aquarium]

I understand Richard,

It just seems very odd to me. I'm an architect, and contrary to public perception that we're all about making things look nice, our first and foremost task is ensuring public safety. As is that of every other professional that works in constructing/managing the built environment. It just seems too odd that this particular part of the built environment is somehow exempt from that goal.