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Thread: What are the differences?

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    In the Industry

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    What are the differences?

    I am a relative newbie to pool ownership, and I hope to assist those on the same road. This particular topic was added at my suggestion, so I am posting first.

    I probably wouldn't have chosen to build a pool, but my pool came with my new house. Now I am delighted to have my own pool! An indoor pool is just what I would have chosen. After all, that makes the pool usable on a rainy day and during the winter. Also cuts down on the leaves and other junk (although I still got storm debris in my pool--it's not a very tight building!)

    Basically, I thought an indoor pool would be easier to deal with than an outdoor pool. True in some ways, not in others!

    UV radiation in sunlight breaks down free chlorine (FC) which is why you need CYA in an outdoor pool to slow down that process. FC lasts longer in an indoor pool--BUT so do the combined chlorines (CC)!! CC's can be very difficult to eradicate from an indoor pool; shocking with chlorine won't eliminate them completely. What you have to do is try to prevent them in the first place.

    To prevent CC buildup, an enzyme treatment helps; there are a number of them on the market. One example is Pool Perfect by Natural Chemistry. The enzymes assist the chlorine in breaking down organic wastes which helps prevent CC formation.

    Another option is the use of non-chlorine shock such as potassium monopersulfate (aka KPMS or potassium peroxymonosulfate). KPMS does NOT remove or break down CC's but it DOES assist in the breakdown of organic wastes. In order for the KPMS to work, it must be present at certain levels in the pool on a continuous basis. This means one more test to run

    There are some other tricky aspects to working with KPMS. One is that the presence of chlorine interferes with the test for KPMS! Well, just use the sodium thiosulfate reagent (Cl neutralizer) before the KPMS test. The other tricky bit is that KPMS can interfere with Cl testing, giving a false high CC reading. To get around that problem, you need a deox reagent which you add to your sample before testing the chlorine.

    Can you use both enzyme treatment and KPMS? As I said I'm a relative newbie. I'm not sure if that's overkill or not! Nobody's told me it's a BAD idea, so at this point I think it's okay.

    Another possible option in an indoor pool is to use bromine. I don't have a great deal of knowledge about bromine, but my understanding is that it is not *quite* as effective a sanitizer as chlorine. It's not used much in outdoor pools b/c, like chlorine, it's broken down by UV radiation. Unlike chlorine, bromine can't be stabilized with CYA or an analog. It's also more expensive than chlorine.

    HOWEVER, bromine does have some advantages! Combined chlorines are problematic b/c they aren't effective sanitizers; combined bromines, OTOH, ARE effective sanitizers! So you don't have to worry about those. The sanitizing efficiency of bromine is also less pH-dependent than that of chlorine. Bromine is also an excellent choice for spas/hot tubs.

    I hope that more knowledgable folks will correct any errors I may have made in this post! At this point I know enough to be dangerous. . . I'm aware that there are gaps in my knowledge, so please feel free to point out my mistakes! I won't be offended.
    ~Jules~

    My pool: INDOOR 13x27 rectangular fiberglass, built ~2001, BBB, TA-60 sand filter, Hayward two speed pump (1 hp/0.33 hp), 3/4 hp booster pump for solar heater
    Taylor K-2006 test

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    divnkd101's Avatar
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    Welcome to the Forum!!!! Thanks for the first post. It is a great category suggestion. Just curious, you are living in Southwest Texas where I can only guess that the average air temp is in the mid/upper 80's. What is your average pool temp (being an indoor pool)?
    MIKE

    21K Inground Custom w/ Spa (Gunite/Plaster), SWCG, Hayward Northstar, Polaris 280, Hayward Color Logics, Jandy PS-8

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    Ha ha. . . I haven't lived here very long, just bought the house in Dec. Pool temp was in the low 50's at that time. I didn't actually get in the pool until last week! Temp was 69; I've been running the solar heater and swam in a nice toasty 77-degree pool last night. This morning it was 75. I'm shooting for upper 80's.

    There's a long story about getting the equipment working and the water in good shape. . . that's been documented elsewhere (poolcenter forum)! I can't really give a meaningful answer, tho, on the avg water temp yet. It stayed in the 50's for some time. It's only been above 60 for about a month!
    ~Jules~

    My pool: INDOOR 13x27 rectangular fiberglass, built ~2001, BBB, TA-60 sand filter, Hayward two speed pump (1 hp/0.33 hp), 3/4 hp booster pump for solar heater
    Taylor K-2006 test

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    Re: What are the differences?

    My responses to your post are in dark blue below.

    Quote Originally Posted by giulietta1
    UV radiation in sunlight breaks down free chlorine (FC) which is why you need CYA in an outdoor pool to slow down that process. FC lasts longer in an indoor pool--BUT so do the combined chlorines (CC)!! CC's can be very difficult to eradicate from an indoor pool; shocking with chlorine won't eliminate them completely. What you have to do is try to prevent them in the first place.

    There are other downsides to not using any CYA in an indoor pool or in a spa, for that matter. Without CYA, the disinfecting chlorine concentration is very high. It's so high, in fact, that it degrades swimsuits much more quickly, has greater corrosion of metals, outgasses chlorine faster so smells more (though it's the "clean" smell of fresh chlorine), and has faster production of monochloramines from ammonia and general disinfection by-products (DPBs) including nasty trihalomethanes (including chloroform) that are carcinogenic. Combined with the lack of good air circulation typical of indoor pools, this has led to higher incidents of asthma and respiratory problems with small children and competitive swimmers, but again only for indoor pools.

    Therefore, using a small amount of CYA in an indoor pool *might* be beneficial to reduce such problems. However, this may make the problem of getting rid of CCs harder, so use of a non-chlorine oxidizer such as KMPS is essential (you talk about that below) which will essentially eliminate the problem of combined chlorines including DPBs.


    To prevent CC buildup, an enzyme treatment helps; there are a number of them on the market. One example is Pool Perfect by Natural Chemistry. The enzymes assist the chlorine in breaking down organic wastes which helps prevent CC formation.

    Another option is the use of non-chlorine shock such as potassium monopersulfate (aka KPMS or potassium peroxymonosulfate). KPMS does NOT remove or break down CC's but it DOES assist in the breakdown of organic wastes. In order for the KPMS to work, it must be present at certain levels in the pool on a continuous basis. This means one more test to run

    What you said was true. KPMS combines with organics BEFORE chlorine gets a chance to, so in a very real sense KPMS prevents CCs from forming in the first place. Also note that the main residual from KPMS is sulfate and these do not leave the water. High sulfates combined with high chloride levels can lead to rapid corrosion of stainless steel. Unfortunately, we don't have data on exactly what these critical levels are.

    There are some other tricky aspects to working with KPMS. One is that the presence of chlorine interferes with the test for KPMS! Well, just use the sodium thiosulfate reagent (Cl neutralizer) before the KPMS test. The other tricky bit is that KPMS can interfere with Cl testing, giving a false high CC reading. To get around that problem, you need a deox reagent which you add to your sample before testing the chlorine.

    Dupont also claims that testing at least 8 hours after addition of KPMS will reduce the interference of the chlorine test, but I am confused by that since a residual that is measurable should interfere with the chlorine test. At any rate, the deox reagent is essential if you are using KPMS.

    Can you use both enzyme treatment and KPMS? As I said I'm a relative newbie. I'm not sure if that's overkill or not! Nobody's told me it's a BAD idea, so at this point I think it's okay.

    I don't know the answer to that either, but remember that an enzyme is a complex organic molecule (a specialized kind of protein) and therefore is subject to oxidation from both chlorine and KMPS. What I do not know is what level of KPMS or chlorine will break down the enzyme and how quickly. My guess is that a shock level of chlorine or the addition of KPMS and up to 8 hours afterwards *may* breakdown the enzymes rather quickly. But I really do not know for sure.

    My guess is that using CYA in the indoor pool would help reduce the problem of chlorine breaking down the enzyme. So that would just leave the KPMS issue. Since KPMS prevents the production of CCs in the first place and since it breaks down organics, *maybe* using KPMS alone is good enough, but again I do not know for sure.

    Another non-chlorine oxidizer is sodium percarbonate, which essentially introduces hydrogen peroxide into the water, but this does not last very long (i.e. has no residual) so is best used to get rid of persistent CCs or to convert a pool from Baquacil to chlorine.


    Another possible option in an indoor pool is to use bromine. I don't have a great deal of knowledge about bromine, but my understanding is that it is not *quite* as effective a sanitizer as chlorine. It's not used much in outdoor pools b/c, like chlorine, it's broken down by UV radiation. Unlike chlorine, bromine can't be stabilized with CYA or an analog. It's also more expensive than chlorine.

    Pretty much true except that you can use a level of bromine such that it is roughly as effective as chlorine. The differences are more what you pointed out in terms of method and cost.

    HOWEVER, bromine does have some advantages! Combined chlorines are problematic b/c they aren't effective sanitizers; combined bromines, OTOH, ARE effective sanitizers! So you don't have to worry about those. The sanitizing efficiency of bromine is also less pH-dependent than that of chlorine. Bromine is also an excellent choice for spas/hot tubs.

    True, but some people are allergic to bromine and others find the smell to be more offensive (though others feel the opposite, so it's probably a personal preference).

    I hope that more knowledgable folks will correct any errors I may have made in this post! At this point I know enough to be dangerous. . . I'm aware that there are gaps in my knowledge, so please feel free to point out my mistakes! I won't be offended.

    I think you did an excellent job!
    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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