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Thread: The Case for 0 CYA

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    The Case for 0 CYA

    CYA significantly reduces UV degradation of FC. But, since more FC is needed when CYA is used, while the FC loss in percentage terms is lower, the chlorine depleltion in absolute terms is more when using CYA than without it.

    This is based on the posts on this forum. The more CYA you use, the more chlorine you use, especially when there's lot's of direct sunlight. I'm not sure that's well understood... Maybe I've got this wrong, but that's what I think the technical data provided by this forum indicates.

    I do understand why CYA is needed with a SWG. The SWG can only generate chlorine at certain rate. It might not be capable of generating chlorine as fast as needed to keep the FC high enough throughout the pool on a sunny day. So, the CYA "holds" chlorine in reserve for when needed.

    However, an automatic chlorinator doesn't have this limitation--or at least it's not an issue for the amount of chlorine that needs dispensing on my 17000 gallon pool on the hottest, sunniest days. It could dose gallons of 12.5% chlorine per hour, if that were needed. Yes, the pump needs to be running, but it's programmed to always be running during the very sunny periods of the day.

    The only real chore I need to do is to fill the Intellichem chlorine (and acid) tank every couple of weeks. I figure if I used CYA, I'd just have to do it more often, since I'd need more FC for the same sanitation. So, why should I use CYA?

    Additionally, when if I need to SLAM the pool, it takes very little chlorine to reach shock level.

    Finally, my dogs use the pool as their watering bowl. Without CYA, the FC needed for sanitation is less than municipal limits on drinking water. Not sure I can say that with CYA added.

    I'd like to know if I'm missing something.
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    Mod Squad pooldv's Avatar
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    Re: The Case for 0 CYA

    The more CYA in the pool the LESS FC gets burned off by the sun. The same pool with 30 cya will use more FC per day than with 50 cya. The other real benefit of CYA is that it significantly buffers the harshness of chlorine. A pool with 1 ppm of FC and no CYA is more harsh than a pool with 70 ppm cya and 28 ppm FC.

    More here about active hypochlorous acid, http://troublefreepool.com/~richardfalk/pool/HOCl.htm
    More here on chlorine/CYA, Certified Pool Operator (CPO) training -- What is not taught
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    Re: The Case for 0 CYA

    You got it half right .... Yes, a higher CYA requires a higher FC level. Yes, a higher CYA level protects a higher % of the FC. But ... even with the higher FC level, the increased protection actually lowers the daily FC ppm loss to the sun.

    And as stated above, the buffering capability of the CYA is very helpful too so that the water is not harsh.

    With 0 CYA, you would have to try to maintain a FC level of 0.1ppm to have the same active chlorine level as the TFP recommended CYA/FC ratio. It is just not feasible to do that without having local spots with not enough FC to prevent algae and to keep the water safe while in use (since that small amount of FC would be quickly consumed.).
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    Re: The Case for 0 CYA

    Let's nail down the most important (to me) consideration first. Does CYA actually reduce chlorine depletion due to UV in absolute terms?

    Please look a the chart below that I posted previously in this thread:

    http://www.troublefreepool.com/threa...rsus-CYA-level




    It shows the more CYA, the more ppm loss. This chart was from ChemGeek, so hopefully he'll chime int.
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    Mod Squad jblizzle's Avatar
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    Re: The Case for 0 CYA

    This was explained in your other thread ... you are ignoring ChemGeeks commentary about the impact of shielding that is not covered in the chart.

    ChemGeeks words:
    Nevertheless, while in theory the absolute loss of chlorine is greater at higher CYA levels (keeping HOCl constant) and is the downside to a "high CYA & high Chlorine" approach, in practice there is some sort of CYA shielding effect such that higher FC and CYA levels at the same FC/CYA ratio lose less absolute amounts of chlorine (see this post later in this thread and see Mark's experiments in this post and this post. However, the primary reason to have higher CYA and Chlorine is to have a sufficient buffer of chlorine to prevent it from dropping to dangerous levels. There is obviously a tradeoff here. Though using no CYA results in the least amount of chlorine loss, the fact is that you simply can't maintain a pool with only 0.05 ppm chlorine everywhere in it -- hence a minimum level is needed as a buffer.
    - - - Updated - - -

    In fact, why did you start another thread for the same discussion?
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    Re: The Case for 0 CYA

    UPDATE : looks like Jason beat me to it....


    Quote Originally Posted by davethomaspilot View Post
    Let's nail down the most important (to me) consideration first. Does CYA actually reduce chlorine depletion due to UV in absolute terms?

    It shows the more CYA, the more ppm loss. This chart was from ChemGeek, so hopefully he'll chime int.
    Dave,

    You're missing a very important point in Richard's post regarding FC loss. The chart you refer to only accounts for loss associated with hypochlorite (OCl-) being destroyed by UV. It's simply a graph generated from equations derived from the chemistry of chlorine photolysis by UV. Richard very clearly states that there is another effect at play here, namely a non-linear shielding effect from the CYA molecule itself regardless of whether or not it has chlorine attached to it. Unfortunately there is no data on this subject in the literature but there is a very real effect at play. When people actually look at FC loss over the long periods of time with high sun, the loss rate is lower than what the chemistry would predict from just UV light destroying OCl- anions. This indicates another effect at play. The idea is that the cyanurate molecule is absorbing some portion of the UV light and re-radiating it at a different wavelength. This is a very common effect in organic chemistry - UV light is absorbed and the energy is either reradiated at a lower wavelength (IR or visible) or the vibrational states of the molecule (phonon radiation) are excited. Richard has proposed some ideas on how to test this but it would require measuring UV light absorption through out the depth of the water column at different CYA concentrations.

    Also, your experience with FC loss may be very different because your pool likely had a fairly significant copper ion load in it from your previous use of the mineral-ion system installed along with your IntelliChem. Copper is a very decent algaecide and you may be getting a benefit from having that metal ion present in your water to help reduce the activity of algae. Just as some people benefit from adding polyquat-60 (algaecide) to their water or doing phosphate removal treatments to make their water less reactive to algae growth, adding copper to one's water will have an effect on algae growth rates and lower the overall burden on your chlorine source. The reason why TFP does not recommend these approaches as a matter of routine pool care is because the benefit of using these procedures (as opposed to just chlorine) does not out-weigh the extra cost and/or possible negative side effects (staining in the case of copper).

    As others have alluded to, there are ways to run a low chlorine pool. Dryden Aqua Systems is a European company (Scottish I believe) that has an entire pool care system that relies on active carbon filtration, coagulation and flocculation, zeolite sand filtration, and injection of small amounts of chlorine and titanium dioxide (to generate hydroxyl free radicals) to act as a filtration and sanitation system. If you design a pool up-front with excellent hydraulics and proper circulation patterns, then you can run a pool according to European standards which calls for no CYA and very low FC levels. That's great for a new pool but most people don't have new pools and most pools built in the US have lousy hydraulics.

    In general terms, TFP exists to teach a method of pool care that is safe, effective and the most widely applicable. Low chlorine methods simply can not work in a "trouble free" way in many types of outdoor pools. I have tinkered around with my pool this season and have gotten some great results lowering my chlorine levels and still having great water (but still requiring the use of CYA). Can the methods I've used apply to everyone...not entirely. So if I share those results it's always with the caveat that there are circumstance to which what I have done just will not apply broadly.

    Stabilizer has to be used in the majority of outdoor residential pools in the US simply by virtue of the way in which these pools are built and operated. It's not really a negotiable idea. So TFP can help people the most by giving them flexible guidelines to follow and that are easy to implement. Zero CYA is really not an option for most people.

    Best wishes,

    Matt

    PS - Richard does not really post on TFP anymore. You are more than welcome to contact him via his external e-mail address (RichardFalk@comcast.net) as I'm sure he would be happy to explain a lot of the technical details that went into his post on water chemistry. He also keeps an extensive list of references that he has used from the literature to shape those ideas and, if you were truly interested in reading about them, you could go and purchase the journal articles on your own (unfortunately for a very steep price as research literature is very costly outside of institutional access).
    Matt
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    Re: The Case for 0 CYA

    ChemGeek has the following written in the article that you are referencing.

    "The following graph combines the two concepts of needing more chlorine at higher CYA vs. the greater protection of chlorine by CYA. The graph shows the total chlorine (FC) loss rate in ppm/hour vs. CYA at different HOCl levels. Remember that this rate of loss will slow down as chlorine gets used up. Nevertheless, [EDIT] while in theory [END-EDIT] the absolute loss of chlorine is greater at higher CYA levels (keeping HOCl constant) and is the downside to a "high CYA & high Chlorine" approach, [EDIT] in practice there is some sort of CYA shielding effect such that higher FC and CYA levels at the same FC/CYA ratio lose less absolute amounts of chlorine (see this post later in this thread and see Mark's experiments in this post and this post [END-EDIT]. However, the primary reason to have higher CYA and Chlorine is to have a sufficient buffer of chlorine to prevent it from dropping to dangerous levels. There is obviously a tradeoff here. Though using no CYA results in the least amount of chlorine loss, the fact is that you simply can't maintain a pool with only 0.05 ppm chlorine everywhere in it -- hence a minimum level is needed as a buffer."

    What it still comes down to is how your pool uses chlorine and you might actually use less overall chlorine with 0 CYA. The biggest deterrent to 0 CYA is the harshness of the chlorine.
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    Re: The Case for 0 CYA

    Matt, I appreciate your comments and agree that most pool owners don't have an automatic chlorination system and good hydraulics. So, use of CYA is probably a must for them.

    Yes, I read that actual chlorine depletion with specific concentrations of CYA is much less than predicted by the theory and charts provided by Chem Geek. Maybe some sort of "shading" or sheilding.

    But, he key takeaway for me was:

    "the primary reason to have higher CYA and Chlorine is to have a sufficient buffer of chlorine to prevent it from dropping to dangerous levels"

    But, with an automatic chlorinator and actual observed chlorine depletion (versus theory) I'm suggesting that this might not be such a concern. The six gallon canister of chlorine that can be dispensed on demand replaces the CYA as a chlorine buffer.

    I also see much less FC depletion in practice at 0 CYA than predicted. It seems like FC depletion is much more a function of water temperature than sunlight. High water temperature causes massive FC depletion! So, theory isn't helping me much when deciding whether to use CYA or how much CYA to use.

    So, I wanted to get as much relevant data as practical by first monitoring the chlorine depletion with 0 CYA. It's easy to add CYA, but I don't know how to reduce it except by water change (which, from my well, has its own mysterious impact). With the actual chlorine depletion I see, I was thinking it just wasn't worth bothering to add CYA.

    I do worry about "harshness", since the FC levels I run are "theoretically" very harsh at 0 CYA (1 - 2 ppm) . But, we certainly can't feel any harshness, nor have our swimsuits deteriorated in any noticeable way. I swim underwater with my eyes open frequently, but I've never experienced any eye irritation. What should I be on the look out for?

    I quit using the copper ionizer in the spring, basedon the advice of forum members. Now copper is around .1 ppm or less.

    Why did I start another thread on the same discussion?

    In another thread (adding well water caused green tint) I was asked about whether I was going to add CYA. The poster then read some more of my threads and said "never mind".

    However, that got me thinking about whether I should experiment with adding CYA. Since I can't come back to 0 CYA easily, I want to quantify what I can before adding CYA.

    Theoretically, more CYA means more chlorine loss. Unless I'm missing something, despite theory, we think CYA reduces FC depletion due to UV based on experimental results from a relatively few number of forum members. Yet we use the same theory to argue that FC can't be maintained at low levels?

    Again, my question was specific to whether it's a good thing to use if one has automatic chlorination and why.

    With automatic chlorination, I 100% agree with:

    "The biggest deterrent to 0 CYA is the harshness of the chlorine."

    So, is there a way to measure "harshness" or its negative impacts in some way?

    In summary:

    I just want to use the minimum amount of chlorine possible to reduce trips to the supplier. Refilling the chlorine tanks is my biggest chore.

    Theory says less CYA means less chlorine depletion, but a few forum members have done experiments that suggest this isn't true, at least at high CYA levels. Experiemental data indicates higher CYA reduces absolute chlorine loss. (I haven't found this quantified anywhere.)

    I have a chlorinator, so it seems like I don't need the buffer CYA normally provides. Maybe my water is too harsh and is impacting something I'm not aware of. I'm willing to collect data and share it on the forum as I go up in CYA.
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    Re: The Case for 0 CYA

    Dave,

    Answer me this Dave - are you still using ORP output as your proxy measurement for FC?

    It's very hard for TFP to trust ORP data as a proxy for FC because we know from the countless experience of other ORP users that they just don't give reliable 1:1 correlations with FC. The consensus opinion in that industry is that an ORP voltage of 650mV or greater implies that the water is able to sanitize pathogens. The problem is, there are so many variables that can confound the ORP voltage that you may think your water is sanitary on the basis of ORP value but, in fact, it is not because the FC is too low and something else is causing the ORP voltage to register higher. Maybe you have a super-stable ORP probe that gives good correlation to FC but that is very far outside the norm of what most users experience.

    What is really needed for your pool are actual FC measurements during the day that shows you are maintaining a 1-2ppm FC. Then those measurements need to be correlated with how much sanitizer is being added to your pool, i.e., the output from the IntelliChem.

    If you want to understand what impact CYA will have, then simply add the lowest measurable amount, 30ppm. You may or may not have some CYA in your pool if any dichlor shock was ever added so the best thing to do would be to add CYA in steps of 10ppm (use liquid CYA, it's more expensive but will be faster to use to raise your CYA) until you achieve a measurement of 30ppm. Then you can repeat the exact same experiment above using 1.5 to 2ppm FC as your target level (5% of 30ppm = 1.5ppm FC). A 5% FC/CYA ratio is what salt water chlorine generator owners use and so it should provide more than enough sanitizing power. You still have to measure FC directly (again, no ORP control) so that your measurements can be compared accurately.

    30ppm CYA is a very low level and will go away fairly quickly in time if you decide using it is unnecessary (replace half the water in your pool and then let the rest get oxidized by chlorine at a rate of 1-2ppm/month).

    A test like that could tell you if CYA is right for you.
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    Re: The Case for 0 CYA

    I recently did an experiment with water at 1,000 ppm FC with no CYA. Every single time I checked the water (multiple times a day) it was at 0.

    I understand this is a very extreme example but in the case of my own pool I've notice a large increase in FC consumption at lower CYA levels, so much that my SWG (which is rated for twice the volume I have) has trouble maintaining the minimum FC level. I raised my CYA to 100 ppm and now run the cell at 25% (was 60% at 70 ppm CYA).

    I don't use ORP because when I did use it, the MV readings fluctuated wildly
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    Re: The Case for 0 CYA

    "Answer me this Dave - are you still using ORP output as your proxy measurement for FC?"

    When I did the experiment to measure FC depletion in full noon time sun, I used the Taylor FAS-DPD drop test. On a daily basis, I note that the ORP level can always be raised at will, even during sunniest day.

    Here's the post from that experiment:

    http://www.troublefreepool.com/threads/116289-FC-at-0-CYA-doesn-t-decay-as-expected

    This is when I first became skeptical of the predicted FC depletion due to UV.

    But, you bring up a good point--My chlorinator uses ORP as a proxy for FC. That's another reason to use as low CYA as possible--the ORP probes get less sensitive as CYA goes up. 0 CYA seems best from a sensitivity viewpoint.

    In my case, the ORP to FC correlation need only be at fixed ph, since PH is tightly regulated by Intellichem. But, I hear you. That's why I maintain almost 10x the required sanitation level, based on Richards' theory for FC at 0 CYA. Yet, I detect no "harshness".

    While that should be "harsh", I think I read city water can be as high as 5.0 FC?

    I will go up in CYA and see what happens. But, I can't easily replace half the water in the pool. I only get 4.5 gph. And, I don't want to add massive amounts of well water until I understand why 6" of well water tinted the pool water green (see separate post:

    http://www.troublefreepool.com/threads/127510-Green-Tint-after-Cooling-Hot-Pool-Water-with-Well-Water


    Thanks!
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    Re: The Case for 0 CYA

    I believe the IntelliChem manual now states you can use 30-50ppm CYA but, I agree, the more CYA you use, the less sensitive the probe becomes because the signal-to-noise ratio goes way down. Call me a skeptic, but I don't trust ORP probes for many, many reasons.

    As I said earlier, I think the only reasonable way to determine what is actually going on is to ignore the probe entirely and use an FAS-DPD test to make precise measurements of total FC levels. If you want, you can double the sample volume used (50mL sample instead of 25mL) and use 3 to 4 scoops of the R-0870 powder to get a pink color. Then the titrant sensitivity would be 0.1ppm/drop. That should be more than enough to make some very precise measurements of FC throughout the day. If you want to record ORP measurements as well, that's fine. I would set the system to some kind of manual dosing mode where you add a very small amount of chlorinating liquid each hour or so and see how the FC fluctuates with time.

    As for "harshness" it's subjective. Everyone seems to react differently to chlorine with some people not noticing it at all to others feeling like their skin has a rash even at the slightest mention of the word chlorine. You'd have to look at something objective over time like swimwear to see if the difference is noticeable and, even then, you would need to swim almost every day to have a good comparison.
    Matt
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    Re: The Case for 0 CYA

    Yes, I agree that I'll need to use the FAS-DPD drop test for measuring actual chlorine loss.

    But first, I'll need to order some more R-0870. Only a scoop or too left, with all the testing I've been doing.

    Good tip on how to raise the sensitivity of the FC test! Can something like this be done for CYA? I read a thread on that, but I think the conclusion was that it couldn't be done, but I don't recall for sure or why not.

    I'll redo everything with 0 CYA before targeting "as low as I can detect" level of CYA and repeat. I'll post somewhere on the site, if anyone's interested in the results.

    Thanks again!
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    Re: The Case for 0 CYA

    The CYA test is what it is. There's no way to make it more sensitive short of using a turbidometer.
    Matt
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    Re: The Case for 0 CYA

    I will go back up and read the intermediary posts from about post number 4 but I want to say that a pool with CyA = 0 is very possible. We did this in the 60's, 70's and 80's. Our pool never got algae and was always crystal clear. We also kept cases of Sodium Hydrochlorite in the garage and tested with an OTO kit at least once a week in the winter and every other day to every day in the summer. Nobody died.

    The thing is that since that time the use of CyA has become the norm and it is a good thing as it buffers the water chemistry and reduces the UV degradation. I would not recommend running a pool without it now as it makes it easier and less costly to do.

    Of course I could be wrong.

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