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Thread: Chlorine Kill Time

  1. #1
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    Chlorine Kill Time

    Does anybody know of a source where I can calculate chlorine kill time given a certain Cyanuric Acid level.. I'm not looking for spot on information just a rough guide.

    For example it is widely accepted that to have a good sanitization level then the free chlorine should be roughly 7% of the cyanuric acid level.. Now please correct me if I'm wrong but does this you give you a kill time of approximately 30 seconds.. So what I'd like to know is that if your Free chlorine level is only 1% of the cyanuric acid levels then what is the kill time for that etc..

    Thanks to any of you guys who can help me on this one.

  2. #2
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    Re: Chlorine Kill Time

    First of all, you need to understand that what I'm about to tell you will be about kill times in lab conditions with planktonic (free-floating) pathogens, not with real pools that have lots of organic matter and high bather loads or that get pathogens in clumps of fecal matter or that are able to form biofilms (if not killed quickly enough), etc. Disinfection rates are normally calculated based on a CT value where this is chlorine concentration (C) in ppm multipled by time (T) in minutes. The table in the PDF file in this link has the CT values for a variety of pathogens.

    Most heterotrophic bacteria have a CT value of 0.08 for a 99% (2-log) kill at room temperature (77F). E.coli is typically quoted as 0.04, though the table shows <0.25 for a 4-log to 8-log kill which translates into a 2-log kill CT of <.06 to <.12. Roughly speaking, at a pH of 7.5 a decent rule-of-thumb is that the equivalent FC with no CYA is equal to the FC/CYA ratio (this is derived in this post). So with an FC that is 10% of the CYA level, most heterotrophic bacteria would get 99% killed in 0.08/0.1 = 0.8 minutes (60*0.8 = 48 seconds) so somewhat under 1 minute. This is why in a commercial/public pool I think an FC that is 20% of the CYA level would be more reasonable so 6 ppm FC with 30 ppm CYA or 4 ppm FC with 20 ppm CYA (not much CYA is usually needed since the high bather load uses up more chlorine than that lost by sunlight so some CYA is good to have but you don't need or want too much). With an FC that is 1% of the CYA level, most heterotrophic bacteria would get 99% killed in 0.08/0.01 = 8 minutes. That might start to be an issue in preventing person-to-person transmission of disease, though it's hard to say.

    Since bacteria typically have a generation (doubling of population) time of 15-60 minutes, preventing uncontrolled bacterial growth needs the 50% kill time to be faster than this. A 99% kill of 8 minutes is roughly a 50% kill time of log10(2)*8/2 = 1.2 minutes so plenty fast enough to prevent uncontrolled growth. (Derivation of the 50% kill rate is described in this thread). So you could have a CT value of 15/1.2 = 12.5 times, so a CT of 0.08*12.5 = 1 which means that any bacteria in the table with a 99% CT less than 1 would get killed faster than it could reproduce. With an FC that is 20% of the CYA level, anything with a CT less than 20 would have its growth stopped. This is why it generally takes a very low amount of active chlorine to keep pools sanitary. The Pinellas County, Florida pool study shows this effect in real pools as described in this thread.

    Remember that viruses don't reproduce in water; they need to be in a host to reproduce. The same is true for protozoan oocysts. So the kill time for viruses and protozoan oocysts is relevant to preventing person-to-person transmission of disease, mostly through the fecal-to-oral route, and not any question of uncontrolled growth since there is none.

    I'm curious -- why do you want this sort of information?

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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  3. #3
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    Re: Chlorine Kill Time

    Richard that is a truly excellent answer and was exactly what I was looking for.

    The reason I needed to know this information was that last season I started working for this pool company which to be honest struggled a bit due to the practice of use tons of stabilised products and when a problem accured throw a ton of chemicals and money at the problem until it went away albeit for a short time.

    So I started working for them and told them flatly that I wanted to look after my pools my way ie the BBB way. They said OK but if the pools turned then I would have to answer.. Well it was a little unfair as most of the pools had been killed to death by stabilised products and I was dealing with pools with 250 to 400+ CYA levels.. Now this was a challenge but I managed and with only one or two pools going milky on me but rectified and cystal clear again within 24 hours, I managed to get through the season fairly unscathed. Now the highest CYA level on any of my pools is 80 PPM with most being 40 - 50 PPM

    Anyway the company have looked at my pools and my chlorine/chemical usage and are now taking note. There has been a huge turn round in the company policy with ALL stabilised products under lock and key unless they can prove a need for them ie to boost CYA levels where levels have dropped below 30 PPM or to aide a new pool.

    So my boss is looking to me as the water expert and I have to write reports on not only his pools but other companies pools. Now one day I mentioned to him that if this particular pool was not drained at least particially the CYA levels would inhibit the Chlorine from doing it's job and then the mistake.. "The chlorine kill time would be such that cross infection between bathers was a real concern". So then he wanted to know what were the kill times on his pools so that he could compare them to the competition and if need be use that information as a sales pitch. Which to be honest I do not have a problem with as I'm only just getting them round to my way of thinking insomuch that it is not our primary job as a pool company to clean pools but to provide a safe and sanitised enviroment for our customers.. A clean and sparkling pool is merely a by product of our primary role.

    Anyway once again Richard many thanks for your help, as always it really is greatly appreciated.

    Oh just so that you know that neither of the links to the poolforum appear to be working.. Could be the site or something so I'll try again later.

  4. #4
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    Re: Chlorine Kill Time

    if you know that much about pools you should be starting your own business...

  5. #5
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    Re: Chlorine Kill Time

    Quote Originally Posted by Freelancer
    Richard that is a truly excellent answer and was exactly what I was looking for.

    The reason I needed to know this information was that last season I started working for this pool company which to be honest struggled a bit due to the practice of use tons of stabilised products and when a problem accured throw a ton of chemicals and money at the problem until it went away albeit for a short time.

    So I started working for them and told them flatly that I wanted to look after my pools my way ie the BBB way. They said OK but if the pools turned then I would have to answer.. Well it was a little unfair as most of the pools had been killed to death by stabilised products and I was dealing with pools with 250 to 400+ CYA levels.. Now this was a challenge but I managed and with only one or two pools going milky on me but rectified and cystal clear again within 24 hours, I managed to get through the season fairly unscathed. Now the highest CYA level on any of my pools is 80 PPM with most being 40 - 50 PPM

    Anyway the company have looked at my pools and my chlorine/chemical usage and are now taking note. There has been a huge turn round in the company policy with ALL stabilised products under lock and key unless they can prove a need for them ie to boost CYA levels where levels have dropped below 30 PPM or to aide a new pool.

    So my boss is looking to me as the water expert and I have to write reports on not only his pools but other companies pools. Now one day I mentioned to him that if this particular pool was not drained at least particially the CYA levels would inhibit the Chlorine from doing it's job and then the mistake.. "The chlorine kill time would be such that cross infection between bathers was a real concern". So then he wanted to know what were the kill times on his pools so that he could compare them to the competition and if need be use that information as a sales pitch. Which to be honest I do not have a problem with as I'm only just getting them round to my way of thinking insomuch that it is not our primary job as a pool company to clean pools but to provide a safe and sanitised enviroment for our customers.. A clean and sparkling pool is merely a by product of our primary role.

    Anyway once again Richard many thanks for your help, as always it really is greatly appreciated.

    Oh just so that you know that neither of the links to the poolforum appear to be working.. Could be the site or something so I'll try again later.
    Excellent
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  6. #6
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    Re: Chlorine Kill Time

    Quote Originally Posted by Freelancer
    Richard that is a truly excellent answer and was exactly what I was looking for.
    :
    "The chlorine kill time would be such that cross infection between bathers was a real concern".
    :
    Oh just so that you know that neither of the links to the poolforum appear to be working.
    I'm glad that BBB is working out for you and that you were able to convince others through sound chemical advice and practical demonstrable experience that it works.

    So how do you maintain the FC levels in your pools without getting CYA to rise? I assume you don't visit your pools more than once a week, do you? Are you using chlorinating liquid (or bleach) with wide swings of FC, but at the higher 80 ppm CYA to minimize chlorine loss from sunlight? Did the pools mostly have pool covers that lowered the rate of chlorine breakdown from sunlight? I'm just curious since we get the question from pool service companies for how to do BBB when you only visit a pool once a week and we don't have great answers for that other than automated systems (peristaltic pump or The Liquidator) or big FC swings or use of some Trihclor tabs with additional dilution and supplemental weekly FC shocking (kind of a hybrid approach), or using a supplemental algaecide weekly such as PolyQuat 60.

    As for kill times, keep in mind that the pool industry uses the "real pools" argument to say that these laboratory kill times don't apply to real pools. There are even some early studies that seemed to show this, but when I looked at them in more detail I noticed that their FC levels were very low (often < 0.5 ppm) and the bather loads high (commercial/public pools) so that it was quite possible the FC got used up combining with ammonia to form monochloramine which is then a reasonably effective algicide and a slower killer of bacteria (though roughly the same as 1 ppm FC with 50 ppm CYA). So that could have helped prevent algae growth and also made kill times independent of CYA level (the kill times were slow, though still fast enough to prevent uncontrolled growth, but seemed to be mostly independent of CYA level). Another argument is what I like to call the "well, nobody died" argument that goes something like the "[no] disease outbreak" phrase used in ANSI/APSP-11 under "Effect of Cyanuric Acid on Chlorine Kill Rates" that may have been put in at the urging of the head of the APSP-11 committee who worked for Chemtura (BioLab, BioGuard, SpaGuard, OMNI, etc.):

    The effect of cyanuric acid on oxidation of organics, kill rates of bacteria and viruses, algae, and protozoa has been demonstrated. Some authorities or standards have suggested adjusting the required chlorine residual to the concentration of cyanuric acid to compensate for the reduction in rates of kill. These studies are not fully comprehensive and applicability to real pools has not been demonstrated. Specifically, we do not have any empirical evidence that a disease outbreak has been linked to a particular cyanuric acid level in a properly sanitized pool (i.e., when at least 1 ppm free available chlorine was present in the pool).
    As with most deceit, it isn't that the above statements are untrue, but I consider the conclusions to be misleading. An outbreak requires enough people to get sick such that there are enough of them to report to their doctors and enough of those doctors to report to their health department. So you generally need some serious uncontrolled bacteria growth before something this extensive is going to occur (Crypto is another matter, but even normal chlorine levels don't inactivate that protozoan oocyst much at all). An increase in transmission from person-to-person is unlikely to show up as an "outbreak" if just a few people near the one sick person also get sick. Also, the Pinellas County, Florida study had 49 out of 486 pools with no chlorine at all and about half of these had high bacterial counts indicating uncontrolled bacterial growth yet there were presumably no "outbreaks" of illness so there isn't a 1-to-1 of uncontrolled bacteria growth with illness.

    The PoolForum links work OK for me so try them again; is anyone else having the problem of accessing The PoolForum?

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  7. #7
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    Re: Chlorine Kill Time

    Links are working fine for me.

    Does anyone else feel feeble, lost or just otherwise real stupid after reading Richards' posts or is it just me?

    Great job Richard! I wish I had half the knowledge you have!

  8. #8
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    Re: Chlorine Kill Time

    Quote Originally Posted by simicrintz
    Links are working fine for me.

    Does anyone else feel feeble, lost or just otherwise real stupid after reading Richards' posts or is it just me?
    I felt feeble, lost and real stupid BEFORE reading Richard's posts.

    The links seem to be working now.
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
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  9. #9
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    Re: Chlorine Kill Time

    Quote Originally Posted by chem geek
    Quote Originally Posted by Freelancer
    Richard that is a truly excellent answer and was exactly what I was looking for.
    :
    "The chlorine kill time would be such that cross infection between bathers was a real concern".
    :
    Oh just so that you know that neither of the links to the poolforum appear to be working.
    I'm glad that BBB is working out for you and that you were able to convince others through sound chemical advice and practical demonstrable experience that it works.

    So how do you maintain the FC levels in your pools without getting CYA to rise? I assume you don't visit your pools more than once a week, do you? Are you using chlorinating liquid (or bleach) with wide swings of FC, but at the higher 80 ppm CYA to minimize chlorine loss from sunlight? Did the pools mostly have pool covers that lowered the rate of chlorine breakdown from sunlight? I'm just curious since we get the question from pool service companies for how to do BBB when you only visit a pool once a week and we don't have great answers for that other than automated systems (peristaltic pump or The Liquidator) or big FC swings or use of some Trihclor tabs with additional dilution and supplemental weekly FC shocking (kind of a hybrid approach), or using a supplemental algaecide weekly such as PolyQuat 60.

    As for kill times, keep in mind that the pool industry uses the "real pools" argument to say that these laboratory kill times don't apply to real pools. There are even some early studies that seemed to show this, but when I looked at them in more detail I noticed that their FC levels were very low (often < 0.5 ppm) and the bather loads high (commercial/public pools) so that it was quite possible the FC got used up combining with ammonia to form monochloramine which is then a reasonably effective algicide and a slower killer of bacteria (though roughly the same as 1 ppm FC with 50 ppm CYA). So that could have helped prevent algae growth and also made kill times independent of CYA level (the kill times were slow, though still fast enough to prevent uncontrolled growth, but seemed to be mostly independent of CYA level). Another argument is what I like to call the "well, nobody died" argument that goes something like the "[no] disease outbreak" phrase used in ANSI/APSP-11 under "Effect of Cyanuric Acid on Chlorine Kill Rates" that may have been put in at the urging of the head of the APSP-11 committee who worked for Chemtura (BioLab, BioGuard, SpaGuard, OMNI, etc.):

    The effect of cyanuric acid on oxidation of organics, kill rates of bacteria and viruses, algae, and protozoa has been demonstrated. Some authorities or standards have suggested adjusting the required chlorine residual to the concentration of cyanuric acid to compensate for the reduction in rates of kill. These studies are not fully comprehensive and applicability to real pools has not been demonstrated. Specifically, we do not have any empirical evidence that a disease outbreak has been linked to a particular cyanuric acid level in a properly sanitized pool (i.e., when at least 1 ppm free available chlorine was present in the pool).
    As with most deceit, it isn't that the above statements are untrue, but I consider the conclusions to be misleading. An outbreak requires enough people to get sick such that there are enough of them to report to their doctors and enough of those doctors to report to their health department. So you generally need some serious uncontrolled bacteria growth before something this extensive is going to occur (Crypto is another matter, but even normal chlorine levels don't inactivate that protozoan oocyst much at all). An increase in transmission from person-to-person is unlikely to show up as an "outbreak" if just a few people near the one sick person also get sick. Also, the Pinellas County, Florida study had 49 out of 486 pools with no chlorine at all and about half of these had high bacterial counts indicating uncontrolled bacterial growth yet there were presumably no "outbreaks" of illness so there isn't a 1-to-1 of uncontrolled bacteria growth with illness.

    The PoolForum links work OK for me so try them again; is anyone else having the problem of accessing The PoolForum?

    Richard

    Richard..

    Firstly I have absolutely no problem with maintaining good FC levels NOW.. I did when I first started purely due to bather load and very high CYA levels as previously mentioned, plus it was the start of summer swim season. As for visiting pools once a week you could not be more wrong.. Winter time when pool temp it 10 - 12 degrees Celsius (roughly 50 degrees Fahrenheit) I visit pools at least twice a week and some times 3 times a week. Spring is 3 times a week and Summer is a minimum of 5 times per week. So you can see the pools get regular visits and rather a lot of 16% liquid chlorine dosed on a regular basis. The pool that has 80PPM of CYA is a SWG pool, all other pools have 60 or less CYA. You are totally correct in answer to companies who enquire about the BBB method for commercial pools. There is absolutely no way on this earth the method will work with just once a week visits without the use of a chlorinator. I really like the look of the Chemiliser CP33 model but that is for another thread. Even on the private pools that I visit twice a week in the summer I leave a container of chlorine for them to put in on the days that I am not there. Between the sun and bather loads I just cannot put enough liquid chlorine in the water to last for at the most 48 hours. However now I have very low CYA levels I can use blocks to aide me on the days that I will not be visiting during the summer.

    Next please believe me when I say you would not believe some of the pools out here in Spain.. Truly dreadful would be a gross understatement.. I have dealt with over the years many people who look after pools and who absolutely no clue as to what they are doing. When I speak to them like I would on this forum they look at me as though I am some sort of alien. The biggest statement I get is that "Well if they sell it at the pool shop then it must be OK". To which I usually reply, "Indeed and when your pool turns green remember to check the price of the chemicals that they are going to sell you to put it right again, only, be fully aware that you will not be putting it right again but merely masking the problem for a short period". Ear infections and quite severe sickness are common place out here especially in the young and elderly. But the biggest problem that I have is trying to convince people that just because the chemicals are sold over the counter it does not make them ok to use all the time. It took me a whole season and outstanding results both athletically and financially to convince the company I work for. As for convincing individuals it takes a little longer but since reading this forum some years ago I can assure you that with the knowledge I have learnt here I have made quite a huge difference in many peoples lives regarding one of their biggest enjoyments here in Spain, their swimming pools.

    So if anybody has any doubts about the methods preached on this forum please let me assure you that not only do they work but they work extremely well. I personally look after 13 pools, 8 of which are communal pools with huge bather loads and I over see a further 100 more and slowly all these pools are getting into balance and producing quality water for our customers.

    Finally as for the Poolforum I have been assured that any IP address from Europe will not work on this site. I'm also a fully qualified computer engineer so know how to get around this and will try again to look at those links that you sent me. The reason I got into doing pools was because I was so sick and tired of being inside all the time I wanted to find a challenging outside job.. Seeing all the green pools here in Spain seemed to be the logical solution and I have never looked back, give me a green slimey pool with an operator who has no clue and you'll never shut me up for hours..

  10. #10
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    Re: Chlorine Kill Time

    Richard further to my last post..

    I do not use any form of anti algae whatsoever with the exception of I do have borates in a number of my pools. The only things that go into my pools are 16% liquid chlorine, 22% acid, sodium bicarbonate and occasionally when CYA drops to 30PPM I will use Triclor blocks or pucks as you Americans call them to get this level back up to 50 PPM.

    Only one of my pools has a cover and that is a SWG pool. FC usage in the winter months is negligible, in the summer it is huge, especially in the large communal pools with huge bather loads. I am just about there in convincing my boss to purchase automatic chlorinators but without them life is very difficult and expensive for the company as the amount of chlorine that I have to use in order to guarantee good sanitization is quite large amounts, up to and including 30 litres per day for a 300,000 litre pool. I know that this is a very high level of chlorine but when you have 200+ PPM of CYA and a boss who will not drain you are caught between the devil and deep blue sea. High FC levels or low sanitization levels with long Chlorine kill times. I chose high FC levels and can assure you that this is far a better choice as I did not have a single complaint about chlorine at all. I calculated that shortly after dosing my FC levels were around the 22 PPM range but reducing quite drastically shortly after so was happy with that.

  11. #11
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    Re: Chlorine Kill Time

    Thanks for the update and details.

    Your more frequent visits to the pools you service explain how this works for you. In the U.S., many pool services just visit their pools once a week which is part of how they get trapped into the Trichlor feeder use as that is clearly the most convenient (if one does not have an SWG or automated dosing system).

    I forgot you were in Spain and that The PoolForum wasn't accessible outside North America. There are many proxy servers you can try such as this one where you should select "us" for the country. I hope that works for you.

    The 22 ppm FC with 200+ ppm CYA would be similar to having only 3 ppm FC with 30 ppm CYA so it's no surprise people didn't notice or complain. It does take a bit of faith in the chemistry to get that high and, of course, we wouldn't want people drinking lots of pool water at that level but that's something they shouldn't be doing anyway. At least in the long run this situation won't last and the CYA levels are getting better managed now that you're on the case!

    Congratulations on your great work and the positive feedback you have given.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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