CYA for Salt Chlorinator Pools II

[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.

[chem geek]

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.

The manufacturers recommend keeping the FC at 3.0 or higher and that this is OK to do for CYA up to 70 and they say you shouldn't go above 100. So from a disinfection point of view at normal pH (7.5), even at 100 ppm CYA the HOCl is 0.012 which is a minimum for disinfection that roughly corresponds to an ORP near 650 mV which is the same level that commercial pools use as a minimum. So the issue is not one of health safety, at least for easy-to-moderate-to-kill bugs (i.e. up to E.coli), but of having sparkling clean pools without algae. Now some in the industry claim that this 3 ppm rate will also prevent algae, but Ben's table and real-world results dispute this (except, perhaps, for SWG pools where the jury is still out on the exact chlorine level needed to prevent algae in such pools).

The study I looked at done by one manufacturer, however, used statistical averages to prove their point saying that the average chlorine level in a group of pools (with varying amounts of CYA) without algae was 3 while in a group of pools with algae the average was below 3. That is, of course, not the right way to look at data. It should be the maximum chlorine level (actually HOCl level) in the pools with algae that is a starting point for analysis. The minimum chlorine level in the pools without algae is also useful and these will likely overlap due to "lucky" pools without enough chlorine but that haven't yet developed algae. Of course, algae growth depends on lots of other factors including nutrients in the pool, sun exposure, rate of introduction of algae into the pool, etc.

So I do not believe that the manufacturers are trying to skirt public safety. My analogy with the tobacco companies was again facetious and way too extreme. A better analogy might be drug companies who promote their solutions rather than non-patentable alternatives that sometimes work as well or better. Also, it could just be that the manufacturers just aren't being as careful with their studies, not intentionally, but just based on who did the study -- these aren't scientifically peer-reviewed articles, but industry conference presentations (the O'Brien paper, on the other hand, was done scientifically with university professors and may have had peer-review).

Richard

[aquarium]

Thanks Richard,

I guess I have a 'lucky pool' then.

Using just bleach and muriatic acid I run it at 1.5-2ppm chlorine as measured with a dumb little OTO test kit, with 30ppm CYA at about 7.2-7.4pH, adjusted via aeration to about 80ppm alk.

Clear blue water.

I mean -really- clear blue water.

TW

[chem geek]

Thanks Richard,

I guess I have a 'lucky pool' then.

Using just bleach and muriatic acid I run it at 1.5-2ppm chlorine as measured with a dumb little OTO test kit, with 30ppm CYA at about 7.2-7.4pH, adjusted via aeration to about 80ppm alk.

Clear blue water.

I mean -really- clear blue water.

TW

An FC of 1.5-2, CYA of 30, pH of 7.3 gives an HOCl of 0.022-0.030 which is probably equivalent to the Min. FC in Ben's chart (not if you look it up directly with his "ranges", but if you convert Ben's chart into HOCl levels, then his Min. FC column is approximately 0.02 or 0.025 though he has it rise up at the lowest CYA levels, probably just to ensure a minimum FC as a reserve). So your pool isn't just lucky, it's also within the relam of the theory we're trying to develop.

On the other hand, Ben has said he has seen pools with algae that were maintained with levels that, after I run through the calculations, are closer to 0.05 ppm HOCl which seems to be the worst-case scenario. So the real answer for algae prevention is likely to be somewhere in that 0.02-0.05 range. Of course, the "real world" creeps in with factors like uneven pool circulation that can cause localized conditions to be worse than the minimum. This is why Ben's chart tries to be conservative -- to account for such conditions.

By the way, what is your CH level and pool water temperature? The saturation index I calculate at 80ºF and 300 CH (with 7.3 pH) would be -0.28 (using my newer index, though the old index is -0.30 so about the same in this case). This isn't horrible and may be a very mild corrosive condition (if you have a plaster pool), but if you want to be in balance, then CH would need to be 700 (with my new index; 600 with the old). Of course once you commit to this high a CH, you have to keep your pH and alkalinity at your current low levels unless you drain your pool water to dilute the calcium.

I try to keep my pool's alkalinity closer to 100-115 with a CH of 260 and a pH of 7.4-7.5 and a water temperature of 88ºF and CYA of 15-20 (hard to tell for sure given the tube stops at 30). My primary motivation for this balance is that the higher alkalinity makes the need for pH adjustment much less frequent, though in practice I hardly ever have to adjust it anyway. I keep an FC level of 2-3 which is safe and conservative since I can drop to 1 FC and still have about 0.020 ppm HOCl similar to your pool. I only lose about 0.5 ppm FC or less per day due to an electric opaque pool cover. I, too, have never had algae and the water is crystal clear blue.

By the way, do you ever get CC > 0 and have to shock your pool?

Richard

[aquarium]

The calcium hardness is about 430ppm.

Arm's length down into the deep end with the pumps running at 3:45PM (full sun in central Texas) the water temp is 84 degrees F.

Plaster pool, about 15,000 gallons, 6 foot deep end.

TW

EDIT: I don't bother with much beyond the OTO test kit, so I don't know CC and I've never shocked since doing BBB starting in June. Just lucky again I guess.

[waterbear]

By the way, what is your CH level and pool water temperature? The saturation index I calculate at 80ºF and 300 CH (with 7.3 pH) would be -0.28 (using my newer index, though the old index is -0.30 so about the same in this case). This isn't horrible and may be a very mild corrosive condition (if you have a plaster pool), but if you want to be in balance, then CH would need to be 700 (with my new index; 600 with the old). Of course once you commit to this high a CH, you have to keep your pH and alkalinity at your current low levels unless you drain your pool water to dilute the calcium.


Richard

Langelier Saturation Index is, IMHO, a bogus measurement for pools. It was designed for closed systems and a pool is an open system. See these posts (2 of mine and one from Ben):
http://www.poolforum.com/pf2/showpos...91&postcount=7
http://www.poolforum.com/pf2/showpos...3&postcount=13
http://www.poolforum.com/pf2/showpos...1&postcount=17