CYA/Chlorine concentration still a contentious debate

svenpup

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Nov 18, 2009
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Re: LOW CYA Chlorine Efficiency

aapetyo said:
The CYA/Chlorine concentration for pools tends to still be a contentious debate among experts. Being a regulator myself I usually get the latest information passed down from the CDC and other agencies. Check out the latest webinar from CDC, particularly the second presenter.

https://services.choruscall.com/links/ppg100504.html
Thanks for the link!

So it sounds like this mysterious, unknown effect of CYA is actually getting some attention. You would think if I have access to this information that every pool supply company would have some insight as well.

I did think it was interesting that he said after hyper-chlorination you have to destroy the excess chlorine. He apparently didn't take into account that the since that the hypochlorous acid is bound into the isocyanurates it is safer to be exposed to higher FC level as a human, in the same way it is safer to be exposed to higher FC level as a microbe.
 

JasonLion

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Re: LOW CYA Chlorine Efficiency

Keep in mind that when someone says hyper-chlorination, they are talking about FC levels of 20+ without any CYA, or way way higher than that with CYA.

{EDIT}Finally someone is talking about raising FC levels in sync with CYA, even if it is only for killing crypto and they say it is a bad idea, at least it came up.{/EDIT}
 

aapetyo

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Apr 22, 2010
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Re: LOW CYA Chlorine Efficiency

"The other problem is that no one is really talking about raising FC levels in sync with CYA levels except for killing crypto."

Really I think the scope of this presentation relates to commercial public pools rather than the private pools. For us health officials, crypto is always the target organism because its resilancy to chlorine disenfection so it is typically used in these type of presentations/studies. However, I think it is important to note that even a private pool (which I also own) should be concerned with handling crypto and unless you are running a well maintained DE filter or a very small micro or nano cartridge filter, hyperchlorination becomes important (for more than one reason). I think this gentleman is suggesting with current research is that CYA levels should be kept lower than previously thought due to FC sequestration and crypto's ability to survive at relatively high FC levels. He goes on to mention that even at 20 ppm CYA that relatively low amounts of FC are available for disinfection. I'd personally like to see some peer reviewed studies showing the ability of the isocyanurate species to replenish the FC as it get used up as others have suggested, or its ability to disenfect in this form. I guess you have to strike a balance with CYA so that you can keep your chlorine in the pool while maintaining disinfection levels of FC. Thoughts?
 

svenpup

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Nov 18, 2009
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Re: LOW CYA Chlorine Efficiency

This topic has gone a little into the deep end, for sure, but...

[rant]
I believe that pool stores pushing stabilized forms of chlorine and then when you bring water in for testing either saying that 100-200ppm is "fine" or not testing for it at all is negligent, bordering on criminal.

You could say (and I guess I would agree) that pool owners should take responsibility for understanding what they need to do to keep their pools safe, but when a whole industry is telling them that trichlor feeders and weekly doses of granular shock are the norm, why should they think any differently? What percentage of test kits sold have a CYA test?

Since I moved to California I have talked to 8 or 10 people who have owned pools for decades. Not one of them has ever heard of Cyanuric acid.
[/rant]
 

JasonLion

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Certainly killing crypto is a serious issue for which there isn't yet a good solution. However, that isn't what jumps out at me personally. My concern/worry is that everyone, in the crypto debate and elsewhere, is either talking about how CYA interferes with chlorine, and their first reaction seems to be to outlaw CYA. Or they are part of the pool industry chorus of CYA, CYA, and more CYA. Neither side seems to ever consider the approach we have taken here of raising the FC level enough to compensate for the CYA.

The presentation in the webinar is neat in that he actually presented data where you could see how our approach can work, at least in principal, at least as well as anything else that has been proposed. But the conclusions he drew from that information were very different, and end up being in opposition, if you will, to our approach. Now certainly, he is talking large public pools, where the issues are different and the economies are different. But the realities are that his line of reasoning will eventually be applied to residential pools, with results that won't be significantly better than the current industry recommendations/practices.

To put it another way, the historical practice has been to simply ignore the effects of CYA completely, leaving pools under sanitized. The new reasoning is that CYA is simply bad and should be avoided if at all possible, so that chlorine can go back to being used the way it was used before CYA existed as much as possible. Neither "side" seems to fathom that you can get the same effective HOCl level by adjusting FC to correspond to CYA in the appropriate way and still get the benefits of having CYA.

If that thinking doesn't get changed, the studies needed to support our approach will not get done, and our approach remains alienated from the whole regulatory framework and the associated standards body recommendations.
 

PaulR

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Jan 11, 2009
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Cupertino, CA
aapetyo said:
I'd personally like to see some peer reviewed studies showing the ability of the isocyanurate species to replenish the FC as it get used up as others have suggested, or its ability to disenfect in this form.
I don't have anywhere near the chops to understand it, but chem geek on occasion points to this as the fundamental paper on the FC/CYA relationship. My takeaway is that the equilibrium between hypochlorous acid and chlorinated isocyanurates goes pretty quickly. I'm sure he'll notice this thread and go into far more detail.
--paulr
 

chem geek

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aapetyo,

I think you should take a look at the "Chlorine/CYA Relationship" section in this thread on my comments on the CPO manual for the CPO course (you can read the other sections as well, if you want). The chlorine/CYA relationship is known science since at least 1974 and there is no real controversy or debate. The only "controversy" is from the chlorinated cyanurate (stabilized chlorine) manufacturers who come up with arguments like "CYA doesn't matter" or that it doesn't matter up to 200 ppm or that they understand the chemistry but don't believe the lab tests apply to real pools or that they disagree with the conclusions or that CYA only protects chlorine breakdown from sunlight so shouldn't be used in indoor pools, etc. Even their own studies (see the Pinellas link in that section) didn't really prove what they wanted in spite of their claims in that study.

The CDC, on the other hand, is looking mostly at killing pathogens including Crypto without regard for other aspects of human health such as the rate of production and quantity of disinfection by-products including nitrogen trichloride. I've sent the CDC links to the source science as well as detailed calculations showing how their own results on Crypto kill times at various CYA levels are predicted from the theoretical chemistry, but I don't think they fully understand that. I just came back from the NEHA conference (that I pay for myself since I am just a residential pool homeowner and do not work in the industry and am doing this completely on my own) and there is still incorrect information being discussed. No one has yet acknowledged that the 10x super-chlorination rule for breakpoint chlorination is wrong when applied to Combined Chlorine (CC) measurements -- the 10x comes from chlorine oxidation of ammonia where ammonia is in different units of measurement than chlorine so that there is a factor of 5 times the 3/2 ratio of chlorine to ammonia on a molar basis. CC, on the other hand, is in the same units as FC and CC already has 1 of the 1.5 chlorine (per ammonia) used for oxidation. This mistake was made decades ago and everyone is repeating it like a bunch of lemmings.

At the conference, there was a woman and her son presenting info about her son's swim team that had many respiratory symptoms (cough, etc.) using an indoor swimming pool with no CYA but that was "in spec". They looked at papers written in Europe ranking improved systems such as using UV to help reduce chloramines and referred to Ernest "Chip" Blatchley's work in this area as well showing UV lowering nitrogen trichloride. When UV was later used in the pool, symptoms dropped by around 2/3rds, yet no one is talking about possibly using a small amount of CYA in the water to significantly lower the active chlorine (hypochlorous acid) concentration to theoretically lower nitrogen trichloride concentrations by orders of magnitude -- that's factors of 10 or more.

As for Crypto, I talked to one presenter who won an award for having the best maintained pool and he uses a multi-faceted approach, mostly having better air circulation, use of non-chlorine shock to supplement oxidation, and significant water replacement. For Crypto, he uses both coagulation with filtration and super-chlorination if needed due to an incident, but when I asked what about person-to-person transmission he said that it really comes down to prevention by not having people with diarrhea enter the pool in the first place. So in practice Cyrpto is a problem whether you have CYA in the water or not. As for being able to super-chlorinate, you can get to your 10 ppm FC for 25 hours by simply having the FC about 10 ppm higher than the CYA level, so 40 ppm FC with 30 ppm CYA or 30 ppm FC with 20 ppm CYA would work (assuming the pH is adjusted to 7.5). There are other methods such as using just 1 ppm of chlorine dioxide overnight, but no one talks about that as a possibility and no manufacturer has ponied up the $1-2 million to get EPA approval for chlorine dioxide in swimming pools, even for this purpose. UV can be used against Crypto, but only through multiple turnovers so it isn't fast (but is still faster than chlorine at normal levels, with or without CYA).

Crypto is not normally an issue in residential pools since they are mostly used by single families who aren't generally going to infect themselves and who tend to be careful about going into a pool when sick. It's an issue for commercial/public pools because one sick person can infect hundreds of people, but again, not having CYA in the water isn't going to significantly affect person-to-person transmission in the short-run (even 4 ppm FC with no CYA takes over 2-1/2 days for a 99% kill) and only makes it easier to super-chlorinate the pool AFTER an outbreak has already been detected (or a diarrhea incident). Yes, chlorine without CYA will kill off Crypto in days compared to over a month, but at the price of higher disinfection by-products, faster oxidation of swimsuits, skin and hair.

In the CPO thread I linked to, take a look at the link on ORP which uses real pool measurements from a public health inspector on hundreds of pools and shows very clearly how ORP is not correlated to FC, but rather to active chlorine (hypochlorous acid, HOCl). This, of course, is not a surprise, but based on additional bacterial sample data he had plus other data I've seen we came to the conclusion that a reasonable "sweet spot" for commercial/public pools would be something like 4 ppm FC with 20 ppm CYA which is roughly equivalent to 0.2 ppm FC with no CYA in terms of sanitation and oxidation rates, but has a chlorine capacity or reserve of 4 ppm. Note that the German DIN 19643 standard is 0.3 to 0.6 ppm FC with no CYA and 0.2 to 0.5 ppm FC if ozone is also used (in the circulation system, since it does not form a residual). They do this to keep disinfection by-products to a minimum, but their system typically uses activated carbon that strips not only all chloramines, but also chlorine itself that must later be re-injected.

Instead of looking at pools with a small amount of CYA being too low in disinfection/oxidation, one should look at pools with no CYA (and 1 ppm FC or higher chlorine levels) as being over-chlorinated and producing too many disinfection by-products (especially nitrogen trichloride) as a result. As Jason points out, different camps are taking completely opposite extremes with no one seemingly taking a rational balanced viewpoint. Instead, it's all or nothing, mostly because there is not a clear understanding of the fundamental chemistry that could be used to guide a rationally informed decision. I have asked multiple researchers to add CYA as a parameter of investigation into their disinfection by-product investigations, but none has done so. If $50,000 fell from a tree, I'd send it to NSPF to add CYA as a parameter to Dr. Blatchley's work (NSPF has been funding much of that work).

Richard
 

chem geek

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With regard to the speed at which chlorine (hypochlorous acid) gets released from CYA, there is a chemical pathway that has half of the chlorine bound to CYA get converted to hypochlorous acid every 1/4 second (see this EPA document on document page 12, PDF file page 18). Since the FC test takes more than a few seconds, it essentially measures reservoir chlorine which is mostly the chlorine bound to CYA. That is, it measures the chlorine capacity or reserve. This is also mentioned in the introductory sections of the 1974 O'Brien paper which definitively determined the chlorine/CYA relationship.

As the numerous links in the CPO thread link I gave showed, the chlorine attached to CYA has minimal disinfection capability and its rate of oxidation is around 1/100th in the study that looked at oxidation of monochlorodimedone. So CYA can be seen as a chlorine (hypochlorous acid) buffer holding chlorine in reserve to be released as needed, but not contributing directly towards disinfection or oxidation. So the use of CYA can be tuned to moderate chlorine's strength. Fortunately, it takes a very small amount of active chlorine to kill most pathogens. It is the protozoan oocysts such as Giardia and especially Cryptosporidium that are more of an issue and with Crypto even not having any CYA at all is not enough. It doesn't make sense to essentially overchlorinate the pool at all times by not having any CYA and having >= 1 ppm FC in a vain attempt at killing Crypto.

As described in this link, CYA skin absorption is minimal so it is very likely that skin absorption of the chlorinated cyanurates is minimal as well.
 

cheddar85

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Feb 18, 2010
271
Houston, TX
Richard, I wanted to say thanks for posting things like this here. Even though I can only wrap my head around about a third of what you post (I was never good at chemistry) I always welcome the chance to learn something new. All the way back from I used to browse PF, I've tried to learn as much as possible from your posts. You've provided a wealth of information to all of us, and I hope you'll be around for a long, long time!

Keep it up! :goodjob: We all appreciate everything you do here!
 

chem geek

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Thanks for the compliment, but the original poster, aapetyo, only posted twice on TFP (both times in this thread) and hasn't responded so my response was obviously not an appropriate post for this discussion (i.e. too technical or confrontational or something).
 

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