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Thread: Shock level

  1. Back To Top    #1

    Shock level

    Ok, let's start with numbers.
    FC 9
    CC 0
    TA 105
    PH 7.6
    CYA 25
    CH 200 (want to raise to around 280 due to fiberglass oxidation, different issue)

    Pool does not get extreme sunlight which is why I keep CYA low. (That plus recent studies suggesting CYA is not a great thing) I AVERAGE about a 1.5 to 3.0 FC loss in a 24 hour period, again depending on clouds, sun, etc. Overnight FC loss is always under 0.5. (Sometimes shows a gain which I attribute to my DPD powder)

    Most pool use is after lunch into late evening.

    Here is my theory and I am looking for feedback and/or suggestions.

    If I can swim safely with FC up to shock level (12+/- based on CYA) why not bring to shock level every night? If FC is 11-12ish in early A.M.and 9-10ish by evening, I use aboout the same amount of 12.5 bleach to maintain as if I were keeping at suggested 5-6 FC. I would never risk an algae bloom sneaking up on me, and would be more than safe if I were to be away for a day or two. The only adverse chemical situation I see is the salt level, which I do not have the proper kit to test.

    Am I missing something? I'm fairly new to BBB. I have a pool that was covered for over ten years. After 2 years of BBB we finally have crystal water. I mean heads/tails dime in ten foot deep end crystal clear.

    Any comments/suggestions are appreciated.
    Thank you!

  2. Back To Top    #2
    Richard320's Avatar
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    Re: Shock level

    Yes, you're missing one key element: UV degradation is a percentage, not a fixed PPM.

    So...currently you're at 9. If you lose 3, that's 33%. If you take it to 12, 33% is 4 ppm. But if you aim for the lower end of safe, say 6, you'll only lose 2 ppm.
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    Re: Shock level

    recent studies suggesting CYA is not a great thing"?
    There hasn't really been anything new on this front in years. The main problem with raising CYA levels is if you don't raise FC levels to compensate. As long as your maintain the two in the proper proportions the kinds of problems mentioned in those studies don't occur.
    why not bring to shock level every night?
    Perhaps because it is more work and more money for no gain.

    Keeping CYA that low in an outdoor pool means you will be using more chlorine and be much closer to a moments lack of attention causing problems. In exchange you gain nothing at all.
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  4. Back To Top    #4

    Re: Shock level

    Thanks, Rich, for the response. I think I get the reasoning. But if I keep it low am I more susceptible to sudden blooms? I have neighbors trees that shed alot of goodies. I also tend to be away on occasion for a day or two. Is the downside of my theory simply more salt added and more bleach purchased?

  5. Back To Top    #5

    Re: Shock level

    Thanks, Lion. You were posting whilst I was replying to Richard. I guess that since I'm testing on a daily basis, and adding 12.5 as needed, I'm thinking adding 20 ounces is the same work as adding 12. Bleach is inexpensive, 2.99 for 128 oz of 12.5. Am I avoiding problems by keeping it high? Or would I have more risk of sudden issues by keeping it low. CYA is good for me here. I have had good luck keeping 25 -30.

  6. Back To Top    #6

    Re: Shock level

    The lower the CYA, the harder it is to keep the FC in the right zone. A higher CYA allows for a larger buffer zone. I prefer to keep the CYA in the 60 to 80 ppm range.

    At any rate, as long as you keep the FC in the 7.5 to 15 % of CYA range, you'll be fine.

  7. Back To Top    #7
    JasonLion's Avatar
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    Re: Shock level

    Quote Originally Posted by elesar
    Or would I have more risk of sudden issues by keeping it low.
    Yes, more risk. That issue isn't insurmountable, careful management will take care of it easily enough. There simply isn't any point in risking it in the first place.

    I am not sure why you think CYA levels around 25 are better, they aren't. If you explained where that is coming from I could explain why you are wrong.
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  8. Back To Top    #8

    Re: Shock level

    I'm not too concerned about being right or wrong about CYA Jason. Reports suggest cyanuric acid can be as adverse as high chlorine levels. Some countries/states prohibit high CYA levels in public pools. I'm not a chemist, so I just look for advice where I can. The BBB method has worked fantastic for me, and my CYA has never been greater than 30ish. I carefully manage the water on a daily basis, vacuum every other day. But I do have occasion to be away for a day or two and have found that keeping FC at the higher level works good for me. My water never smells like chlorine, and I have no adverse reactions to blondes and swimsuits. I was sinply wondering if there was something I was missing regarding my theory.

  9. Back To Top    #9

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    Re: Shock level

    Please don't write "reports suggest..." without providing references. You clearly heard or read this information somewhere, so please provide links to it so that we can see the details of what you have read and can more intelligently respond to it. As far as I know, when the CDC or industry pundits refer to higher CYA levels being a problem, this is because they have no clue about the chlorine/CYA relationship (determined definitively in 1974 in this paper) so assume that the FC level remains constant at some 1-3 ppm recommended level. In that situation, then of course a higher CYA is problematic, but if the FC is raised proportionately with the higher CYA, then the active chlorine level that kills pathogens, prevents algae growth, and oxidizes bather waste is nearly identical in concentration.

    The only state in the U.S. that bans CYA for all commercial/public pools is New York and that was due to a Crypto outbreak where they, quite frankly, overreacted (I believe it was after the massive Milwaukee outbreak in 1994, even though that wasn't via swimming pools). Even without CYA, normal FC levels are insufficient to protect against Crypto, but they mistakenly thought that they could not treat pools with superchlorination when CYA was present (based on CDC studies). So now they not only use more chlorine in their commercial/public outdoor pools due to losses from sunlight, but also create more disinfection by-products and oxidize swimsuits skin and hair much faster and corrode equipment. All because of a lack of understanding of the chlorine/CYA relationship. However, many states also ban CYA in indoor pools due to a similar lack of understanding of the chlorine/CYA relationship and a mistaken belief that CYA is only needed to protect chlorine from breakdown from sunlight and not understanding that CYA significantly moderates chlorine's strength (i.e. it's too high without CYA, unless the FC is very low, much lower than 1 ppm).

    As for other countries, they generally do not ban CYA, but CYA is not used in the DIN 19643 standard used in some commercial/public pools in Europe. However, the FC level in that standard is 0.3 to 0.6 ppm with no ozonator or 0.2 to 0.5 ppm with an ozonator so they have at least some basic understanding of how higher active chlorine levels lead to the problems I described above. They don't use CYA because they use activated carbon in the circulation path to remove chlorinated disinfection by-products, but that also removes chlorine which must be added again after the carbon filtration. If CYA were used, the FC level would need to be higher and that would mean more chlorine removed by the carbon filter and added back after the carbon filter so would be more expensive and impractical.

    It's your pool and you can do what you want, but if you do lose chlorine from sunlight then there's really no good reason for the lower CYA level. A higher CYA level with proportionately higher FC level would have the same active chlorine level but your daily FC loss would be lower. There are limits for this since at higher CYA levels it will take more chlorine to SLAM the pool if there is a problem. A decent compromise for non-SWG pools is in the 40-50 ppm range. Some people in very sunny areas go higher and indoor pools or other pools with no sun exposure go lower.
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    Re: Shock level

    Very interesting explanation of CYA relationship. A lot of information, so I'll need to read it again. I never realized there could be different requirements for commercial pools. In the winter months, I swim in health center pools. I have been shocked watching buckets of chlorine being poured into health center whirlpools. My swimsuits have fallen apart in short order in indoor pools. The chlorine smell is often strong. I will admit, the bather loads are high during aerobic classes... 30+
    Lucy
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    Re: Shock level

    The problems with faster degradation of swimsuits, flakier skin, frizzier hair, more volatile, smelly and irritating nitrogen trichloride, faster metal corrosion are all due to a higher active chlorine level because CYA is not used yet the FC is still >= 1 ppm. The bather load increases the amount of disinfection byproducts, including nitrogen trichloride, but the other problems with high active chlorine levels are independent of bather load.

    My wife experienced the same sort of problem when she swam in a commercial indoor pool over 5 months of the winter season with 1-2 ppm FC and no CYA and her swimsuits would degrade (elasticity get shot) in just one season we we'd have to buy new swimsuits every year. Her skin was flakier and hair frizzier so she had to use de-chlorinating shampoo right away. In our own outdoor residential pool over 7 months of the summer season with 3-6 ppm FC and 40 ppm CYA, her swimsuits lasted for 7 years and the effects on skin and hair were much less noticeable. The difference was the active chlorine level which was 7 to 30 times higher in the pool without CYA compared to our pool.

    The Chlorine/CYA relationship is not the only basic piece of scientific fact that the pool/spa industry doesn't fully understand. You can read about other issues in the thread Certified Pool Operator (CPO) training -- What is not taught. CPO training is required in many (but not all) states for commercial/public pool operators. It's a great program, but as you can see, it's not perfect.
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  12. Back To Top    #12
    Lrooth's Avatar
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    Re: Shock level

    Now I can explain to my water aerobic friends why their swimsuits fall apart in the Heath club pool and not mine! It has been part of many discussions while swimming in the pool. Thanks.
    Lucy
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  13. Back To Top    #13
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    Re: Shock level

    I don't see much difference between CYA 25 and 30, the lower limit of the recommendation. I stick as close as I can to the recommended FC for ease and cost -- every gallon that doesn't go in the pool is a gallon I don't have to tote home from the store.
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  14. Back To Top    #14

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    Re: Shock level

    The low end of the recommendation does not mean that is as optimal for saving chlorine. If you have 5 ppm FC with 50 ppm CYA, you will lose LESS chlorine than if you have 3 ppm FC with 30 ppm CYA. This is due to a non-linear CYA effect that we don't fully understand, but have measured. 30 ppm only makes sense if there is not much sun so much less chlorine loss from sunlight.
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  15. Back To Top    #15

    Re: Shock level

    Not sure how this post was hijacked by the CYA police, but I understand. It just gets so tedious. Thanks Richard320 and JamesW for your simple and direct answers to the original question. You provided food for thought that I will chew slowily.

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    Re: Shock level

    Quote Originally Posted by elesar
    Not sure how this post was hijacked by the CYA police, but I understand. It just gets so tedious. Thanks Richard320 and JamesW for your simple and direct answers to the original question. You provided food for thought that I will chew slowily.
    This topic has 246 views, and leaving comments like
    (That plus recent studies suggesting CYA is not a great thing)
    without responses or corrections will lead others into reading that as true. Then there will be people with low CYA wondering why they are losing half their FC.

    The other thing is the BBB method is more about knowledge. Testing your own water and knowing what all the numbers mean specifically, and I looked at it as they were just trying to make sure you fully understand what CYA is and its purpose and how it relates to proper chlorine levels and chlorine loss. You also did already get a perfect answer to your question from Richard.

    Bottom line is if you want to try to lower the amount of chlorine your losing, you should raise your CYA, if your happy where your at,


    It just gets so tedious.
    CYA is good for me here. I have had good luck keeping 25 -30.
    I am curious what led to these comments regarding CYA levels. Cya should only change with water dilution, and it sounds like your trying to be too exact with it and over testing it. Basically more worried about the proper level than you need to be. As long as your not using any dichlor/trichlor granuals or pucks...you don't have to worry about it going too high which is the most important thing. Personally I test once, calculate and add to get to 40 and treat it as 40 until I test a few months later and raise it back to 40 if its lowered with rain and splashout/refill.
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    Administrator Leebo's Avatar
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    Re: Shock level

    Alright......let's take this thread back onto topic. If it keeps going in the direction it's heading.....it will quickly disappear.


    Quote Originally Posted by elesar
    Here is my theory and I am looking for feedback and/or suggestions.

    If I can swim safely with FC up to shock level (12+/- based on CYA) why not bring to shock level every night? If FC is 11-12ish in early A.M.and 9-10ish by evening, I use about the same amount of 12.5 bleach to maintain as if I were keeping at suggested 5-6 FC. I would never risk an algae bloom sneaking up on me, and would be more than safe if I were to be away for a day or two.
    Even at 5-6FC you will kill off any normal algae quicker than they could start. IF you are planning on going away for a few days, THEN toss in some extra bleach. If you're able to test and add daily, keep it on the low end and save some cash. If you are really worried about your FC dropping low and an outbreak starting look into an algaecide. It's not really needed if you keep all the numbers in check....but if adding a dose here and there helps you sleep at night, then it maybe worth the extra cost.

    Key point.....don't overthink things here......it's just water!

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    Re: Shock level

    I have locked this thread. There is absolutely nothing to be gained by trying to teach someone who isn't the least interested in learning.
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