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Thread: Effective CYA

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    Effective CYA

    Quote Originally Posted by duraleigh View Post
    Yes. You should probably bring your CYA up to aroun 60ppm or so per SWG's recomendations. Most of them suggest about 60-80. That'll cut down your FC loss..

    Secondly, I would suggest an overnite FC loss test. If you need info on how, post back. It'll determine if you have organic material in the pool.

    Third, how does your water look?

    I think the CYA curve flattens pretty quickly at around 20ppm as far as chlorine retention in sunlight goes so there are few benefits to going too much higher. In fact, something like 80% of chlorine retention is achieved at the 10-12 ppm CYA level.There are however three really big negatives to going much higher than about 30-40 ppm CYA:

    1) The higher the CYA value the less "active chlorine" there is available at the same free chlorine level and it's "active chlorine" and not free chlorine that kills.

    Example: At a CYA of 0.0 ppm (no CYA in pool), and say, 4 ppm free chlorine, you have a full 4 ppm of "active chlorine" (chlorine with the ability to kill) but little reserve because there is no CYA to stabilize or to "bank" the chlorine. At 20ppm CYA and the same 4 ppm chlorine, your active chlorine might be only 0.1 ppm and that's not a typo. This is because at 20 ppm CYA, something like (ballpark) 95% of the free chlorine is bound to the CYA and of the remaining 5%, only half of that or 2.5% has effective killing power (assumes Ph around 7.5). This means that 2.5% of the initial 4 ppm chlorine (or about 0.1 ppm) is available as active chlorine and the rest is "banked" by the CYA. The CYA will release more chlorine but only after the front line chlorine (active chlorine) is depleted. Fortunately, only about 0.06-0.15 ppm active chlorine is required to kill more than half of the germs so 20 ppm CYA is a "nice spot" to be at since it shields chlorine from sun, has reasonable kill times and good Oxidation Reduction Potentials (ORP's).

    2) Increasing the CYA levels increases substantially the time required for chlorine to kill. With no CYA I think the chlorine kill times are less than a few seconds. At CYA levels of 30-80 ppm the kill times are (ballpark) several minutes to an hour or more.

    3) And finally, the oxidation reduction potential drops as CYA increases, and flattens at about 70 ppm CYA. Add as much chlorine as you like and beyond about 70ppm CYA the active chlorine tops out at about 0.18-0.2 ppm. This level is sufficient to kill but kill times are VERY long, ORP's are low and a LOT of chlorine must be added (about 14 ppm free chlorine to obtain 0.1 ppm active chlorine, something like that). Compare this to 20 ppm CYA where you only need 4 ppm free chlorine to get this same 0.1 ppm active chlorine and you get much faster kill times and higher ORP's.

    So here's where people get into trouble: they use stabilized chlorine and with each application they increase their CYA levels and don't increase their free chlorine to compensate for rising CYA levels. When CYA levels finally get too high, virtually all of the chlorine is bound to the CYA and very little active chlorine is available. If you keep chlorine levels constant and let CYA continue to climb, the active chlorine decreases to the point where "bad things" multiply faster than you can kill them. With little active chlorine and an ever increasing number of bacteria and algae, all the active chlorine is consumed thus causing the CYA to release more and more chlorine to replenish the lost active chlorine, thus depleting the chlorine bank. Your test kit (when you measure free chlorine) will show free chlorine plummeting because it is consuming an ever increasing amount of bacteria. Shortly after this happens your free chlorine goes to zero and you begin to see cloudy/green water appear. The solution is to drain water, refill to lower CYA levels to about 10-40 and to only use unstabilized chlorine (sodium hypochlorite, calcium hypochlorite or lithium hypochlorite) from then on. The 10-40 ppm CYA range is enough to protect chlorine from the sun while still providing a good chlorine "bank" and high enough active chlorine levels, reasonably fast kill times and good oxidation reduction potential levels.

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    Re: How quick does chlorine dissipate?

    Your first 2 points are only true if the FC is not raised when the CYA level climbs. If one proportionally raises the FC to keep the FC/CYA ratio constant, then the active chlorine level is kept constant, the rate of killing pathogens and algae and oxidizing bather waste remains constant, and the ORP remains the same. Your third point of "Add as much chlorine as you like and beyond about 70ppm CYA the active chlorine tops out at about 0.18-0.2 ppm." is absolutely positively not true. That is not how chemical equilibrium works. 3 ppm FC with 30 ppm CYA has the same active chlorine level as 10 ppm FC with 100 ppm CYA or 50 ppm FC with 500 ppm CYA.

    You are also wrong in terms of CYA's protection of chlorine. Yes, a large amount of benefit occurs with lower CYA levels but that's because chlorine goes away very quickly with no CYA. It is not true though that higher CYA levels flatten out in the protection. There is a non-linear CYA (or chlorine bound to CYA) shielding effect of UV from lower depths that more than makes up for the higher FC level at such higher CYA levels. See the table in this post as an example of loss rates as a function of CYA all at the same FC/CYA ratio (active chlorine level). You will see that from 30 ppm CYA to 50 ppm CYA the chlorine loss rate drops by 16% and from 50 ppm CYA to 80 ppm CYA it drops by 25%. Mark on this forum did experiments described in this post and this post that showed how much higher CYA levels lowered chlorine loss rates. He did these experiments because we noticed people having lower chlorine loss at higher CYA levels but the same FC/CYA ratio.

    It sounds like you are quoting some standard pool industry lore that claims that CYA doesn't have any significant chlorine protection at higher levels, but it's simply not true. Could it be that you are quoting (without attribution) from the PPOA article Cyanurics - Benefactor or bomb? where it says the following falsehoods:

    This chart shows reasonable retention achieved with only 5 ppm CYA in use. Over 80% of all the retention potential available is achieved at 10 ppm, while values much over 20 ppm CYA exhibit diminishing returns, soon appearing beyond the cost-effectiveness threshold.
    :
    Stated simply, as CYA exceeds 70 ppm, virtually any level of chlorine will result in no more than about .2 ppm equivalent effectiveness.
    :
    Another surprise: As effectiveness (in terms of ORP) is lost with rising cyanuric concentration, a flattening of the curve occurs around 70 ppm CYA; here’s where no appreciable additions of chlorine will make any difference in the resultant level of ORP!
    You cannot mix what someone writes online because it's something they believe as someone who promoted ORP sensors (that's what Kent Williams used to do) vs. looking at real science in actual detail. Not just real science, but real observations as shown in the graphs in this post that show that ORP does not stop climbing at high CYA levels. On that graph includes 21.6 ppm FC with 90 ppm CYA for a calculated HOCl of 0.145 and a measured ORP of 703 mV (regression calculated is 742 mV). When pools are SLAMed with 40% FC/CYA ratios, they have roughly 0.3 ppm HOCl and yellow/mustard SLAM has around 0.7 ppm HOCl. There is, however a problem with most ORP sensors since their membranes get fouled at higher CYA levels especially in the presence of sunlight (for reasons not yet understood though I have speculated on them elsewhere). This post derives why the FC/CYA ratio is proportional to the active chlorine level with no limit on CYA, no flattening out, etc.

    Now for manually dosed pools the risks above 50 ppm in terms of the amount of FC needed for a SLAM should have one question whether one should have a higher CYA level, but for SWG pools the risk is less since they are automatically maintained and the benefits of lowering the SWG %ontime are greater for reducing the rate of pH rise and having the SWG cell last longer. In a pool exposed to sunlight, 20 or 30 ppm CYA is going to have significant chlorine loss. Also, with manual dosing and one needing to dose higher, the higher CYA level means that such extra 2-3 or 4 ppm FC above the minimum isn't as much as a proportion of CYA. That is, if you had only 20 or 30 ppm CYA you may need to add 4 or 5 ppm FC over the minimum so would be at 6 or 7 ppm FC so 20% or 30% FC/CYA ratio. Compare this to being 3 or 4 ppm FC over the minimum at 50 ppm CYA so 7 or 8 which is 14-16% over the minimum.

    Most people don't keep their FC/CYA level at double the minimum 7.5%. They add enough chlorine so as not to go below the minimum when one doses the next day. With usual 2-3 ppm FC per day usage the dose is around that much higher or a bit more. This has nothing to do with killing more than half of the bacteria and algae because if one maintains at least the minimum then there is virtually no bacteria or algae at all. It is killed faster than it can reproduce. The amount of algae spores blown in is small so there is no need to have double the minimum FC/CYA level.
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    Re: How quick does chlorine dissipate?

    You said: the rate of killing pathogens and algae and oxidizing bather waste remains constant, and the ORP remains the same.

    comment: If you fix the free chlorine and let CYA levels climb (by using stabilized chlorine), you run into the case where there is too little active chlorine to kill germs and they overwhelm the chlorine. You then get plummeting chlorine levels and soon after you get poor water and algae. Also, kill times do increase with rising CYA levels.

    You said: Your third point of "Add as much chlorine as you like and beyond about 70ppm CYA the active chlorine tops out at about 0.18-0.2 ppm." is absolutely positively not true. That is not how chemical equilibrium works. 3 ppm FC with 30 ppm CYA has the same active chlorine level as 10 ppm FC with 100 ppm CYA or 50 ppm FC with 500 ppm CYA.

    comment: at ever increasing CYA levels, more and more of the chlorine is bound. At 4 ppm chlorine and 20 ppm CYA the active chlorine is ballpark 0.1 ppm. Raise the CYA to 70 ppm and it takes about 20 ppm chlorine to get the same amount of active chlorine so, within reason of what most people will ever use, even 20 ppm chlorine will only get you to about 0.1 ppm active chlorine. It would take 40ppm free chlorine to get 0.2 ppm and within reason, most people won't do this so I stand by my comment.

    Also, why would you subject bathers to a higher level of CYA than is necessary just for marginal increase in chlorine retention? 10-20 ppm CYA gives good chlorine protection, reduces bather exposure to unnecessary levels of chemicals (CYA), lowers the exposure to free chlorine you must add (4ppm chlorine for 20 ppm CYA vs 20 ppm chlorine required a 70 ppm CYA to get the same active chlorine levels) and so on. The less chemicals in a pool the better off bathers are.

    You said: Most people don't keep their FC/CYA level at double the minimum 7.5%. They add enough chlorine so as not to go below the minimum when one doses the next day.

    comment: I think they do, if they're smart. At 30 ppm CYA, 7.5% yields about 2 ppm chlorine and it takes 4 ppm to yield 0.1 ppm active chlorine which is needed to ensure thorough killing. They claim the threshold required is only about 0.05 ppm or so but one should error on the higher side of 0.1 ppm. Also, don't some agencies such as the UN or the World Health Organization require more than this such as 0.1 to 0.15 ppm? Thanks.

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    Re: How quick does chlorine dissipate?

    Chemgeek. The Lincoln county NE health web site agrees with my assertion that kill times lengthen as CYA levels climb with fixed chlorine levels.
    http://www.lincoln.ne.gov/city/healt...f/Cyanuric.pdf

    They state: At above 50 ppm of cyanuric acid, thetime it takes to kill bacteria in the water is longer compared to swimming pool water withoutcyanuric acid. Also, as the level of cyanuric acid builds up, the chlorine will becomeincreasingly less effective in keeping the water clean and problems such as increased cloudinessand exceeding combined chlorine limits can occur.

    They also state:
    A 2007 study3 by the Centers for Disease Control and Prevention(CDC) revealed that cyanuric acid significantly diminishes chlorine’s ability to inactivate thechlorine-resistant protozoan, cryptosporidium. Based on the findings of the CDC study, theLincoln-Lancaster County Health Department recommends that cyanuric acid levels not exceed30 ppm.

    The above seems to be inline with my post.

    Your thoughts? Thanks.

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    Re: Effective CYA

    Simple. Everybody is allowed to be wrong. You don't have to be right to get your wrong ideas printed and followed. You only have to to pay the right person. So who do you trust? The person with a vested interest or the one that just wants to promote a proven and working system?

    Heck, people think the world is flat and only a few thousand years old. You are free the think whatever you want. Just don't expect it to be correct.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Effective CYA

    Quote Originally Posted by pabeader View Post
    Simple. Everybody is allowed to be wrong. You don't have to be right to get your wrong ideas printed and followed. You only have to to pay the right person. So who do you trust? The person with a vested interest or the one that just wants to promote a proven and working system?

    Heck, people think the world is flat and only a few thousand years old. You are free the think whatever you want. Just don't expect it to be correct.
    Comment: You telling me ALL these references are wrong??? :

    1) http://www.lowrycg.com/wp-content/up...Pool-rev03.pdf

    "The rate of killing algae is directly proportional to the HOCl concentration. Therefore, the total chlorine concentration is relevant only to ensure that the sole killing form of chlorine HOCl is not depleted. The amount in reserve has nothing to do with the rate of killing algae only the concentration of HOCl matters for that.This concentration is roughly proportional to the FC/CYA ratio. Remember the soldier analogy–it doesn't matter if you've got millions of soldiers in reserve if you've only got a handful on the front lines doing the actual killing."

    Translation: rate of killing is reduced when you have small amounts of active chlorine


    2) Or figure #3 in this one:

    http://www.ppoa.org/pdfs/PrP_Cyanuri...0or%20Bomb.pdf

    that shows increased kill times required as CYA levels increase for the same active chlorine


    3) or this one from the Lincoln county (Nebraska) health department:

    http://www.lincoln.ne.gov/city/healt...f/Cyanuric.pdf

    "A 2007 study by the Centers for Disease Control and Prevention (CDC) revealed that cyanuric acid significantly diminishes chlorine’s ability to inactivate the chlorine-
    resistant protozoan, cryptosporidium. Based on the findings of the CDC study, the Lincoln-Lancaster County Health Department recommends that cyanuric acid levels not exceed 30 ppm'

    and others.....they're all wrong. Right? Right.......

    It has nothing to do with a persons right to believe whatever they want. At some point there is enough evidence to say one way or the other.



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    Re: Effective CYA

    Yes, they come from the same, flawed root. Therefore are all wrong or suspect.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Effective CYA

    Freetothink,

    Please list your pool information in you sig like we ask all members to do. That way we can see this information readily when you need help with your pool.

    Also, we ask that people put a city and state so we can see the climate they are in. What does "fl/fl" mean?
    Dave S.
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    Re: Effective CYA

    Will do. Naples FL

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    Re: Effective CYA

    Quote Originally Posted by freetothink View Post
    Comment: You telling me ALL these references are wrong??? :

    1) http://www.lowrycg.com/wp-content/up...Pool-rev03.pdf

    "The rate of killing algae is directly proportional to the HOCl concentration. Therefore, the total chlorine concentration is relevant only to ensure that the sole killing form of chlorine HOCl is not depleted. The amount in reserve has nothing to do with the rate of killing algae only the concentration of HOCl matters for that.This concentration is roughly proportional to the FC/CYA ratio. Remember the soldier analogy–it doesn't matter if you've got millions of soldiers in reserve if you've only got a handful on the front lines doing the actual killing."

    Translation: rate of killing is reduced when you have small amounts of active chlorine


    2) Or figure #3 in this one:

    http://www.ppoa.org/pdfs/PrP_Cyanuri...0or%20Bomb.pdf

    that shows increased kill times required as CYA levels increase for the same active chlorine


    3) or this one from the Lincoln county (Nebraska) health department:

    http://www.lincoln.ne.gov/city/healt...f/Cyanuric.pdf

    "A 2007 study by the Centers for Disease Control and Prevention (CDC) revealed that cyanuric acid significantly diminishes chlorine’s ability to inactivate the chlorine-
    resistant protozoan, cryptosporidium. Based on the findings of the CDC study, the Lincoln-Lancaster County Health Department recommends that cyanuric acid levels not exceed 30 ppm'

    and others.....they're all wrong. Right? Right.......

    It has nothing to do with a person has a right to believe whatever they want. At some point there is enough evidence to say one way or the other.



    Yes, they are all wrong as is your assertions because they all rest on flawed proposition, namely that you hold to a fixed FC level. This assertion is typical in the pool industry, i.e., that all pools should be maintained at an FC level between 2-4ppm irrespective of CYA level.

    That is NOT what is taught here. TFP teaches that pool owners need to maintain a constant FC/CYA RATIO which is ~ 7.5%. That way, no matter what type of pool you have or where you live, we all have the same active chlorine (hypochlorous acid) level. Thus, my SWG pool running at 80ppm CYA is the same as an above ground pool back East running at 30ppm CYA. As long as we are both maintaining the same FC/CYA ratio, then our active chlorine concentrations are the same. Please go back and reread chemgeek's posts and link as you are clearly making this mistake over and over again in your responses. You are constantly saying that a high CYA level is bad but you are assuming that the FC level remains fixed. This is also why TFP teaches the use of manual bleach chlorination or SWG's because use of puck floaters and puck feeders leads to precisely the problem you describe - an ever increasing CYA level with little or no change in the target FC level.

    As well, your assertions seem to be based on the underlying notion that "chemicals are bad". That is a matter of your personal opinion and not good public health science. Please show me a study, any study from a reputable public health agency, that demonstrates swimming in a pool with 100ppm CYA is bad for your health. When you can find a peer-reviewed paper that shows a clear link between the chemicals used in swimming pools (at levels found in swimming pools) and adverse health reactions, then we can talk about changing levels.

    You are also quoting from regulatory agencies, but you have to realize that those agencies are tasked with regulated public/commercial pools where bather loads are very high and the risk of person-to-person disease transmission is a very real problem. The methodologies used to maintain public pools are typically incompatible and unnecessary when talking about residential, private pools. That is why in the USA, for the most part, private residential pool care methods are not regulated by federal or state agencies (except for construction purposes).

    Please review the TFPC Method of pool care by going through the links in Pool School and some of the advanced links chemgeek has posted. Most of your arguments are based on a complete misunderstanding of the methodologies taught here.
    Matt
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    Re: Effective CYA

    Quote Originally Posted by freetothink View Post
    Comment: You telling me ALL these references are wrong??? :

    1) http://www.lowrycg.com/wp-content/up...Pool-rev03.pdf

    [FONT=sans-serif]"The rate of killing algae is directly proportional to the HOCl concentration. Therefore, the total chlorine concentration is relevant only to ensure that the sole killing form of chlorine HOCl is not depleted. The amount in reserve has nothing to do with the rate of killing algae only the concentration of HOCl matters for that.This concentration is roughly proportional to the FC/CYA ratio. Remember the soldier analogy–it doesn't matter if you've got millions of soldiers in reserve if you've only got a handful on the front lines doing the actual killing."
    If you are going to quote him, you should read all his papers. While as been pointed out, more of what he has written is directed at a commercial pool application he has a fairly good handle on his science. Try this paper: http://www.lowrycg.com/wp-content/up...eed-rev-03.pdf

    Here is his first paragraph
    How Much Free Chlorine Do You Really Need?
    By Robert W. Lowry
    If you look at any guideline or standard or check with any health code, you will see that almost all of them recommend a free chlorine (FC) level of 2.0 to 4.0 ppm.
    This gives rise to the idea that if you measure free chlorine in the water and it is between 2.0 and 4.0 ppm then the water is OK or safe. It may or may not be. There is a way to know how much free chlorine you need in any pool.
    The answer is FC needs to be a minimum of 7.5% of the CYA level – unless supplements are used
    He talks about supplements including algecide said, minerals and a host of other things you can add to reduce this 7.5% ratio. They are all valid. Add enough copper and you don't need to worry about algae, but don't invite your blond friends to swim. Everything we put in our pools come with a cost. TFP is all about understanding the cost associated with each product and allow you to choose which is best for your situation.

    You will note he supports our teachings that FC must be at least 7.5% of CYA. As a matter of fact, much of what he has written seems to come out of our teaching.

    When it comes down to it, your pool is yours to treat as you see fit.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: How quick does chlorine dissipate?

    Quote Originally Posted by freetothink View Post
    You said: the rate of killing pathogens and algae and oxidizing bather waste remains constant, and the ORP remains the same.

    comment: If you fix the free chlorine and let CYA levels climb (by using stabilized chlorine), you run into the case where there is too little active chlorine to kill germs and they overwhelm the chlorine. You then get plummeting chlorine levels and soon after you get poor water and algae. Also, kill times do increase with rising CYA levels.
    I don't disagree, but what I wrote before what you quoted was "If one proportionally raises the FC to keep the FC/CYA ratio constant" which means that one CAN keep consistent disinfection, algae prevention, and oxidation by managing the FC/CYA ratio. In other words, looking at either FC or CYA alone is the wrong thing to do. Yes, for those using stabilized chlorine sources having the CYA rise then not increasing FC proportionally is a problem, but I don't want anyone thinking the pool industry mantra "CYA doesn't matter; only FC matters" or the opposite "CYA is bad" are true because neither are.

    Quote Originally Posted by freetothink View Post
    You said: Your third point of "Add as much chlorine as you like and beyond about 70ppm CYA the active chlorine tops out at about 0.18-0.2 ppm." is absolutely positively not true. That is not how chemical equilibrium works. 3 ppm FC with 30 ppm CYA has the same active chlorine level as 10 ppm FC with 100 ppm CYA or 50 ppm FC with 500 ppm CYA.

    comment: at ever increasing CYA levels, more and more of the chlorine is bound. At 4 ppm chlorine and 20 ppm CYA the active chlorine is ballpark 0.1 ppm. Raise the CYA to 70 ppm and it takes about 20 ppm chlorine to get the same amount of active chlorine so, within reason of what most people will ever use, even 20 ppm chlorine will only get you to about 0.1 ppm active chlorine. It would take 40ppm free chlorine to get 0.2 ppm and within reason, most people won't do this so I stand by my comment.
    You are missing the point that it takes a VERY low active chlorine level to kill pathogens and a somewhat low active chlorine level to prevent algae growth. See the chart in this post that shows the times for 3-log reductions (99.9% kill) when the active chlorine level is the same as 0.1 ppm FC with no CYA at pH 7.5 so roughly a 10% FC/CYA ratio. The fact is that commercial/public pools in the U.S. with no CYA in them are by state law required to have at least 1 ppm FC and therefore are OVER-CHLORINATED because their active chlorine level is much higher than needed for disinfection and algae prevention. It means that swimsuits, skin, and hair are getting oxidized much faster and disinfection by-products are created faster. My wife has personal experience with this effect where she used to swim in a community center indoor pool with 1-2 ppm FC and no CYA over each winter season and we'd have to replace the swimsuits used (elasticity got shot) each season whereas in our private outdoor pool with 3-6 ppm FC and 30-40 ppm CYA the swimsuits would last for 7 years and the differences in her skin and hair between the two pools were very noticeable. It is such a big difference that we are now spending lots of money gas heating our pool through the winter so that she can use it.

    Now if you are buying into the Kent Williams PPOA school of thought then you will say that you have to have higher chlorine levels for oxidation of bather waste but there are two problems with that. First is that for residential pools the bather load is so low that one does not need higher chlorine levels to handle bather waste, particularly for outdoor pools exposed to sunlight because the UV that breaks down chlorine produces hydroxyl radicals that are very powerful though short-lived oxidizers. Second is that when chlorine reacts with bather waste it produces disinfection by-products and higher chlorine levels not only produce them faster but can produce more of the most irritating and volatile nitrogen trichloride. The better approach is to use supplemental oxidation systems (such as ozone) or coagulants (such as SeaKlear PRS Stage 1 and 2) to remove the organic precursors without using chlorine to do so.

    Europe understands this and in DIN 19643 specified only 0.3 to 0.6 ppm FC with no CYA with no ozone or 0.2 to 0.5 ppm FC with no CYA with ozone. They can't use CYA because their system uses coagulants (iron or alum) and activated carbon filters to remove organics and disinfection by-products from the pool (and such methods would tend to remove CYA as well). In the U.S., commercial/public pools could operate with a 20% FC/CYA ratio for a rough equivalent of 0.2 ppm FC with no CYA and have plenty of disinfection for everything except Crypto which isn't handled well even when there is no CYA in the water. The SeaKlear PRS I mentioned will coagulate Crypto and the CDC Model Aquatic Health Code (MAHC) requires secondary disinfection systems such as UV or ozone in high-risk venues to deal with Crypto. Instead of superchlorinating, one could get rid of Crypto overnight using chlorine dioxide generated on-site by adding sodium chlorite to chlorinated water (ideally with CYA in it since the lower active chlorine level minimizes generation of chlorate).

    Quote Originally Posted by freetothink View Post
    Also, why would you subject bathers to a higher level of CYA than is necessary just for marginal increase in chlorine retention? 10-20 ppm CYA gives good chlorine protection, reduces bather exposure to unnecessary levels of chemicals (CYA), lowers the exposure to free chlorine you must add (4ppm chlorine for 20 ppm CYA vs 20 ppm chlorine required a 70 ppm CYA to get the same active chlorine levels) and so on. The less chemicals in a pool the better off bathers are.
    If you read what I wrote, it's not marginal but significant. Having 1.5 ppm FC with 30 ppm CYA in a pool compared to 4 ppm FC with 80 ppm CYA has around 60% higher chlorine loss. You are again missing the fact that the protection of chlorine from sunlight is NOT just due to the chlorine bound to CYA but also from a non-linear shielding effect such that higher CYA levels even with proportionally higher FC levels uses less chlorine. You seem to be stuck on the PPOA charts when the reality is NOT those charts and this has been proven not only in observations of thousands of real pools but in bucket and spa experiments.

    What are you talking about reducing bather exposure to CYA? CYA does not absorb through the skin (see this paper), is not volatile, and is less toxic than ordinary table salt (see this link).

    You also are missing that how much chlorine you add is based on how much you lose, NOT on the absolute FC level. I am NOT proposing high CYA levels for commercial/public pools. Most of their chlorine usage is due to bather load, not loss from sunlight. So 20% FC/CYA levels with 4 ppm FC with 20 ppm CYA or 6 ppm FC with 30 ppm CYA is reasonable. Most CYA test kits only measure down to 20 or 30 ppm CYA anyway. However, in residential pools, most chorine loss is from sunlight, not bather load, so protecting chlorine from sunlight DOES reduce chlorine demand and does so significantly.

    Quote Originally Posted by freetothink View Post
    You said: Most people don't keep their FC/CYA level at double the minimum 7.5%. They add enough chlorine so as not to go below the minimum when one doses the next day.

    comment: I think they do, if they're smart. At 30 ppm CYA, 7.5% yields about 2 ppm chlorine and it takes 4 ppm to yield 0.1 ppm active chlorine which is needed to ensure thorough killing. They claim the threshold required is only about 0.05 ppm or so but one should error on the higher side of 0.1 ppm. Also, don't some agencies such as the UN or the World Health Organization require more than this such as 0.1 to 0.15 ppm? Thanks.
    Most people don't operate their pool at 30 ppm CYA unless its an indoor pool where 20-30 ppm CYA may be used. For outdoor pools exposed to sunlight, most on this forum operate in the 40-50 range and those with SWG pools are closer to 80 ppm CYA. My pool is lower in CYA because I have a mostly opaque pool cover but that means a lower chlorine loss of only 1 ppm FC per day.

    Where are you getting that 0.1 ppm FC equivalent is needed "to ensure thorough killing"? That simply isn't true. Look at the chart I linked to above where you can see the kill times at 0.1 are very fast where for fecal bacteria it's a 3-log reduction (99.9% kill) in 1-1/2 minutes or less. Having half that rate of kill would still be fast. I'm not talking about commercial/public pools where a 20% FC/CYA ratio (e.g. 4 ppm FC with 20 ppm CYA for indoor pools or 6 ppm FC with 30 ppm CYA for outdoor pools) may be more reasonable (i.e. 0.2 ppm FC equivalent), but residential pools where the risks are far lower especially for person-to-person transmission of disease.

    Where are you getting the U.N. or WHO recommendation of 0.1? Are you talking about the WHO document Guidelines for safe recreational water environments - VOLUME 2 SWIMMING POOLS AND SIMILAR ENVIRONMENTS? Even that document has things in it that are simply not true such as the following:

    High levels of cyanuric acid cause a situation known as ‘chlorine lock’, when even very high levels of chlorine become totally locked with the cyanuric acid (stabilizer) and unavailable as disinfectant; however, this does not occur below cyanuric acid levels of 200 mg/l.
    So even these people at WHO don't understand chemical equilibrium. There is no such thing as chlorine lock. If you raise the FC proportionally with the CYA level you retain the same active chlorine level. Chemical equilibrium is defined by RATIOS of concentrations of chemicals. The ratio of (in simplistic terms) [HOCl]*[CYA]/[Cl-CYA] is a constant and since most of FC is bound to CYA (so is Cl-CYA in what I wrote) then increasing FC (so Cl-CYA) proportionally when CYA increases keeps HOCl (hypochlorous acid) constant.

    The WHO document also has the incorrect 10x rule that was misapplied to Combined Chlorine (CC) when it is only correct for ammonia in ppm Nitrogen units. It is incorrect when applied to CC because 1) the units of measurement for CC are in the same units as FC, namely ppm Cl2 which is a factor of FIVE larger then the units for ammonia which is ppm N, and 2) one chlorine is already attached to the ammonia (I already went over this with you in the thread Breakpoint Chlorination).

    Destroying chloramines requires free chlorine levels at least 10 times the level of combined chlorine.
    This WHO document does not talk about 0.2 ppm -- it says instead 1 ppm FC but is silent about CYA level and doesn't understand that CYA is a hypochlorous acid (active chlorine) buffer and therefore one doesn't need 1 ppm FC levels of active chlorine. The distinction between having chlorine in reserve vs. the active level is lost on most in the pool industry.

    For a conventional public or semi-public swimming pool with good hydraulics and filtration, operating within its design bathing load and turnover and providing frequent (or online) monitoring of chlorine and pH, experience has shown that adequate routine disinfection should be achieved with a free chlorine level of 1 mg/l throughout the pool.
    Even DIN 19643 goes lower than this though as you might imagine it is almost impossible to adequately maintain 0.2 ppm FC throughout a pool without outstanding circulation. Pools in the U.S. tend to have much worse circulation so using CYA in moderation allows one to have an ample FC buffer while tuning the FC/CYA ratio for adequate disinfection.
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    Re: How quick does chlorine dissipate?

    Quote Originally Posted by freetothink View Post
    Chemgeek. The Lincoln county NE health web site agrees with my assertion that kill times lengthen as CYA levels climb with fixed chlorine levels.
    http://www.lincoln.ne.gov/city/healt...f/Cyanuric.pdf

    They state: At above 50 ppm of cyanuric acid, thetime it takes to kill bacteria in the water is longer compared to swimming pool water withoutcyanuric acid. Also, as the level of cyanuric acid builds up, the chlorine will becomeincreasingly less effective in keeping the water clean and problems such as increased cloudinessand exceeding combined chlorine limits can occur.

    They also state:
    A 2007 study3 by the Centers for Disease Control and Prevention(CDC) revealed that cyanuric acid significantly diminishes chlorine’s ability to inactivate thechlorine-resistant protozoan, cryptosporidium. Based on the findings of the CDC study, theLincoln-Lancaster County Health Department recommends that cyanuric acid levels not exceed30 ppm.

    The above seems to be inline with my post.

    Your thoughts? Thanks.
    They are not comparing constant FC/CYA ratios. They are taking a constant FC and then noting that higher CYA levels result in slower kill times. So what is your point? We already know that the kill times are related to the active chlorine level and that this is proportional to the FC/CYA ratio. Why don't you look at the numerous scientific peer-reviewed papers in respected journals I list in the "Chlorine/CYA Relationship" section of the first post in the thread Certified Pool Operator (CPO) training -- What is not taught. They show how kill times depend on the active chlorine level and I've mapped those studies to calculated HOCl levels and found them all to be consistent (except for the one algae study that is flawed).

    You need to understand that for whatever reason, hardly anyone in the pool industry nor governments nor even some researchers apparently even understands the most fundamental basics of equilibrium chemistry when it comes to chlorine and CYA -- something taught in high school, let alone college. The paper defining the equilibrium constants came out in 1974. I think the main problem has been that there isn't just a single chemical reaction, but rather 9 chemical reactions (6 are independent from each other) for chlorine bound to CYA, 3 chemical reactions for CYA alone, and 1 chemical reaction for chlorine unbound to CYA and that this throws people into a tizzy even though they could simply plug in the numbers into MINEQL+ or do what I did and create a Pool Equations spreadsheet (though incredibly tedious to do) and spit out the result. Or they could just do some basic simplification as I did in this post that nets out to the following rough approximation for the dominant reaction:

    HClCY- + H2O <<<---> HOCl + H2CY-
    "Chlorine Bound to CYA" + Water <<<---> "Active Chlorine" + "Cyanurate Ion"

    and knowing that the ratio of the items (excluding water that isn't included in equilibrium constants because its concentration is constant) is a constant could trivially derive the FC/CYA ratio as a rough proxy proportional to the active chlorine level. [HOCl]*[H2CY-]/[HClCY-] is a constant (at a given temperature and ionic strength). Since most chlorine is bound to CYA, this becomes [HOCl]*CYA/FC = constant or [HOCl] = constant * FC/CYA.

    Again, I don't think it unreasonable to limit CYA in commercial/public pools. There's an ongoing debate about that but except for Crypto the actual CDC surveillance studies for outbreaks as well as past pool studies don't show significant increases in disease spread even at fairly low FC/CYA ratios. This is due in part to the fact that most bacteria are fairly quickly killed by even low chlorine levels and is also due in part to having higher bather load produce enough ammonia to have monochloramine which isn't moderated in its strength by CYA. Of course, one shouldn't count on having such CC for disinfection purposes.

    So the question for commercial/public pools is where to draw the line. Should it be 30 ppm? 50 ppm? 100 ppm? Or should instead the real rule be the FC/CYA ratio since that determines the actual disinfection and oxidation rates? I think the FC/CYA ratio is the better approach and that will naturally limit the CYA level based on economics. Of course, there's the issue of the EPA with its 4 ppm FC maximum that gets in the way, but some states have higher FC limits for pools (see this post showing Florida and Wisconsin allowing 10 ppm FC, Texas 8 ppm FC, and California with no limit).
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  14. Back To Top    #14

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    Re: Effective CYA

    Quote Originally Posted by freetothink View Post
    Comment: You telling me ALL these references are wrong??? :

    1) http://www.lowrycg.com/wp-content/up...Pool-rev03.pdf

    "The rate of killing algae is directly proportional to the HOCl concentration. Therefore, the total chlorine concentration is relevant only to ensure that the sole killing form of chlorine HOCl is not depleted. The amount in reserve has nothing to do with the rate of killing algae only the concentration of HOCl matters for that.This concentration is roughly proportional to the FC/CYA ratio. Remember the soldier analogy–it doesn't matter if you've got millions of soldiers in reserve if you've only got a handful on the front lines doing the actual killing."

    Translation: rate of killing is reduced when you have small amounts of active chlorine


    2) Or figure #3 in this one:

    http://www.ppoa.org/pdfs/PrP_Cyanuri...0or%20Bomb.pdf

    that shows increased kill times required as CYA levels increase for the same active chlorine


    3) or this one from the Lincoln county (Nebraska) health department:

    http://www.lincoln.ne.gov/city/healt...f/Cyanuric.pdf

    "A 2007 study by the Centers for Disease Control and Prevention (CDC) revealed that cyanuric acid significantly diminishes chlorine’s ability to inactivate the chlorine-
    resistant protozoan, cryptosporidium. Based on the findings of the CDC study, the Lincoln-Lancaster County Health Department recommends that cyanuric acid levels not exceed 30 ppm'

    and others.....they're all wrong. Right? Right.......

    It has nothing to do with a persons right to believe whatever they want. At some point there is enough evidence to say one way or the other.


    Bob Lowry in the first link got that info FROM ME. And it's consistent with what I have been saying about the FC/CYA ratio so I am completely missing your point. I wrote that the rate of killing WAS proportional to the active chlorine level. Why do you think I said anything different?

    The Benefactor or Bomb does NOT show the same active chlorine level. It shows increasing CYA at a CONSTANT FC level and that lowers the active chlorine level. Note that Figure #3 shows very low FC at 0.1 ppm and that 0.5 ppm kill times were not nearly as long (roughly 5 times faster as would be expected). At an FC/CYA ratio of just 5% so roughly equivalent to 0.04 ppm FC with no CYA, the 99.9% kill time is less than 4 minutes though in that chart it would be the same as 0.5 ppm FC with 10 ppm CYA which looks more like under 1 minute. Don't you think it deceitful that Kent used an example of 0.1 ppm FC for the chart to show how slow the kill when CYA is used? The original paper HAD to use such low FC levels because one can't as easily see the slowdown in kill time otherwise! Also, some of those charts in that article (ones looking at ORP) are plain wrong since they reflect only what he was seeing with his older ORP sensors that maxed out at higher CYA levels.

    Again, what is your point since you completely mixed up what I was saying. I have always said that the active chlorine level is what determines the kill times and that the active chlorine level is proportional to the FC/CYA level. However, the active chorine level is NOT the FC level and perhaps that is where you are mixed up.

    Again, read the scientific peer-reviewed papers in respected journals I linked to in the CPO thread. They demonstrate that higher CYA when not raising the FC results in slower kill times, BUT a constant FC/CYA ratio results in the same kill times because the calculated HOCl predicts those kill times. And of course, this makes sense since its based on fundamental equilibrium chemistry where for chlorine and CYA this has been known definitively since at least 1974.
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  15. Back To Top    #15

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    Re: Effective CYA

    Quote Originally Posted by pabeader View Post
    Yes, they come from the same, flawed root. Therefore are all wrong or suspect.
    Quote Originally Posted by JoyfulNoise View Post
    Yes, they are all wrong as is your assertions because they all rest on flawed proposition, namely that you hold to a fixed FC level. This assertion is typical in the pool industry, i.e., that all pools should be maintained at an FC level between 2-4ppm irrespective of CYA level.
    The first link from Bob Lowry is fine and much of that information came from me (via Bob looking at my posts and then my reviewing his document via E-mails with Bob in March, 2012).

    The PPOA article has a lot of good info in it but not all of it is correct or applicable. It was biased towards ORP sensors since that's was Kent Williams' background (see this post from Ben Powell about Kent's background and ties to Stranco, an early manufacturer of ORP sensors).

    Lincoln-Lancaster County can certainly suggest a maximum of 30 ppm and as I've written for commercial/public pools having a lower CYA limit is reasonable because most chlorine loss is from oxidizing bather waste and not from sunlight, but that does not apply to residential pools which is mostly what we are talking about.

    freetothink, you talk about evidence, but you search for that which supports your position instead of looking for factual information in peer-reviewed scientific papers in respected journals plus basic science and consistency with over 90,000 members at TFP plus the nearly half a million visitors to this site every month during peak swim season. There's a reason these things work and that the FC/CYA ratio proportional to the active chlorine level that determines disinfection, algae prevention, and oxidation works. It's because it's the truth based on real science, not just someone's opinion.

    I also don't think we're in a big disagreement since at one point you seemed to understand the FC/CYA relationship, that if you were to raise the FC proportionally at higher CYA levels that you would have the same active chlorine level and therefore the same disinfection and oxidation rates. At first you referred to some PPOA information that said this was not true, that at some magical CYA level no amount of FC would produce a higher active chlorine level (based on what Kent saw with his ORP readings), but that simply is not true. His ORP sensors didn't work properly at high CYA levels for reasons having nothing to do with the actual active chlorine level (maybe CYA itself interfered with the membranes used in his sensors). This is not the first time we've seen ORP not work well and a search on this forum will give you plenty of examples of why ORP is questionable. See ORP Control and ORP Probe Failing; Current in the Water; Bonding Issue? for two recent issues with SWG pools and ORP drifts high regardless of chlorine concentration and ORP and chlorine where the latter shows diurnal variation where ORP drops 50+ mV during the day but goes back up at night in spite of maintaining the active chlorine level (same FC and CYA). Also, in an earlier link I showed with ORP data that 30 out of 130 pools with more than one ORP sensor on the same pool showed 100 mV or more differences between the sensors measuring the same water!.

    I think the only point of disagreement is where exactly to limit the CYA level. I think that having a minimum FC/CYA ratio for commercial/public pools would make sense and that a natural CYA limit will come out of that out of practical economic considerations where in higher bather load pools a lower CYA level would make more sense while in low bather load pools a higher CYA level may make more sense. For residential pools (outdoors with no cover), a higher CYA level may make more sense but "higher" does not mean 100+ ppm. And, of course, you can do whatever you want for your own pool. If you want to operate it at 20 ppm FC and use more chlorine as a result of greater losses in sunlight, that's up to you. If you search on threads on this forum you will see the opposite where people in hot sunny areas are pushing their CYA up higher with proportionally higher FC in order to use less chlorine per day. This is non-intuitive because the non-linear CYA shielding effect is, well, non-intuitive as are most non-linear effects (our brains understand linear proportions well, but don't handle non-linearity very well especially when there are multiple counteracting effects).
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    Re: Effective CYA

    This is the most fascinating game of table tennis I've watched in a long while.


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  17. Back To Top    #17

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    Re: Effective CYA

    Quote Originally Posted by Megsyperk View Post
    This is the most fascinating game of table tennis I've watched in a long while.
    If you like back-and-forth, see The forgotten alternative sanitizer for pools and spas that was extensively studied.
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    Re: Effective CYA

    Quote Originally Posted by chem geek View Post
    O holy night, that was positively euphoric.


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    Re: Effective CYA

    Now my head hurts!!
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    Re: Effective CYA

    So, I'm confused... Nothing new

    Isn't saying that a FIXED FC will be less effective as CYA rises just proving the entire point?

    I'm more confused about going back to other sources also only studying, or testing, a fixed FC.

    I call pool store shill!!!
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