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Thread: DiChlor vs Bleach

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    DiChlor vs Bleach

    Quote Originally Posted by chem geek
    6% Clorox Regular is 5.71% Available Chlorine (by weight) and is 6.17% "Trade" % which is the % Available Chlorine by volume. Most chlorinating liquid is quoted by Trade %. The rule that one gallon raises the FC in 10,000 gallons by the same numerical value as the percentage of chlorine is technically referring to the Trade %. So one gallon of 6% Clorox in 10,000 gallons raises the FC by 6.17. The "6%" in Clorox is the weight percentage of sodium hypochlorite in an ingredients list. It's confusing, but fortunately all these numbers are close enough to each other to not make this a big deal.

    You seem to know what your talking about so I'll ask
    How does 6% clorox compare to soduim di-chlor say at 62%? Gallon:Lb?
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    Re: CYA from 60 to 0 ppm

    Quote Originally Posted by kiksroks
    How does 6% clorox compare to soduim di-chlor say at 62%? Gallon:Lb?
    There are two forms of Dichlor, the more common being dihydrate since it is safer to transport and store (it's less flammable) and is 55.4% Available Chlorine if pure (i.e. if 100% Dichlor). One gallon of 6% bleach is equivalent in resulting Free Chlorine (FC) to 14.9 ounces weight of Dichlor (dihydrate) or 9 ounces weight of Trichlor or 12.8 ounces weight of Cal-Hypo 65%.

    Of course, for every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.
    For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm.
    For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

    The above 3 rules are independent of concentration since they relate the amount of CYA or CH to the amount of FC.

    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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    Re: CYA from 60 to 0 ppm

    Quote Originally Posted by chem geek
    There are two forms of Dichlor, the more common being dihydrate since it is safer to transport and store (it's less flammable) and is 55.4% Available Chlorine if pure (i.e. if 100% Dichlor). One gallons of 6% bleach is equivalent in resulting Free Chlorine (FC) to 14.9 ounces weight of Dichlor (dihydrate) or 9 ounces weight of Trichlor or 12.8 ounces weight of Cal-Hypo 65%.

    Of course, for every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.
    For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm.
    For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

    The above 3 rules are independent of concentration since they relate the amount of CYA or CH to the amount of FC.

    Richard
    So with the weaker di-chlor it is almost 1lb=1gal.
    Thanks! how do you come up with this stuff?

    So say I've got 0 fc in my scg pool (due to heaver bather load, dirty cell, space wolves, whatever) and the cya is at 80 ppm (max recommended by scg manufacturers) and I add enough di-chlor to get 10ppm fc; What effect would the additional 9ppm of cya have on my pool.
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    Re: CYA from 60 to 0 ppm

    Quote Originally Posted by kiksroks
    So with the weaker di-chlor it is almost 1lb=1gal.
    Thanks! how do you come up with this stuff?

    So say I've got 0 fc in my scg pool (due to heaver bather load, dirty cell, space wolves, whatever) and the cya is at 80 ppm (max recommended by scg manufacturers) and I add enough di-chlor to get 10ppm fc; What effect would the additional 9ppm of cya have on my pool.
    The answers to your questions are all just chemistry. It's something the industry should have been teaching in CPO courses and telling pool stores, but the stabilized chlorine folks apparently didn't want you to know exactly how much CYA you were adding when using their products nor to tell you that this becomes a problem in terms of algae prevention (unless you use a supplemental algaecide which is partly why they offer them in "algae-free guaranteed" kits).

    If you've already got 80 ppm CYA and you use enough Dichlor to get to 10 ppm FC, then the additional 9 ppm CYA that it adds will raise your CYA level to 89 ppm. A one time dose like this isn't horrible, but if you do this regularly then your CYA level can keep climbing and that can lead to algae growth if you don't raise the FC level proportionately. If you see this table in The Pool School you will see that roughly speaking it is the FC/CYA ratio that determines the amount of "active" chlorine and therefore the amount of chlorine you need to prevent algae. SWG pools can get by with a lower ratio due at least in part to their automated more consistent dosing (and possibly also due to some super-chlorination of part of the water in the SWG cell).

    If you need to add more chlorine to your pool and already have enough CYA, then you should use unstabilized chlorine. Chlorinating liquid or unscented bleach won't add anything you don't want, though it will increase the salt level by more than other sources of chlorine. For every 10 ppm FC added by chlorinating liquid, bleach, or lithium hypochlorite, it also increases salt levels by 8 ppm beyond that of all chlorine sources (all chlorine sources increase salt by 8 ppm when the chlorine gets used up so chlorinating liquid, bleach, etc. add a total of 1.6 ppm salt accounting for addition and consumption of their chlorine).

    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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    Re: CYA from 60 to 0 ppm

    I've read the articles and follow health department guidelines but I think that the effects of cya on the effectiveness of sanitizers are still somewhat up in the air and possibly grossly exaggerated. I don't have any studies or numbers to back this up but I have a ton of real world experience. I'll leave it at that.

    I'm new to this forum and seeing people post about adding 17 gallons clorox to their pools seems very strange to me when a simple application of 10lbs of di-chlor would be so much more convenient and effective. A rise of 9ppm or even 20ppm in cya has virtually no effect on sanitation and would not affect their pools in any way. It will after all need to be replenished at some point anyway. Yet to avoid it they will go buy cases of clorox and lug literally hundreds of lbs of liquids around. I don't get it.

    All of the cya problems I've seen in my pools have been from little or no cya. I can't say I've ever told a customer "I'm sorry your pool is green ma'am it's gotta be the stabilizer, the cya levels are too high!" I'm sorry people but in my experience cya does not turn your pool green.
    I understand that at some point too much can be a problem, but jeez guys if you have to shock your scg pool 2 or 3 times a year it's not going to hurt to use one ten lb. bucket of di-chlor and it will be much easier and more effective than 17 gallons of bleach. to avoid

    For the record I do not sell Chlorine, I run a pool service and repair company and am responsible for the maintenance of a large number (you would be surprised) of residential pools.
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    Re: CYA from 60 to 0 ppm

    Quote Originally Posted by kiksroks
    I've read the articles and follow health department guidelines but I think that the effects of cya on the effectiveness of sanitizers are still somewhat up in the air and possibly grossly exaggerated. I don't have any studies or numbers to back this up but I have a ton of real world experience. I'll leave it at that.

    I'm new to this forum and seeing people post about adding 17 gallons clorox to their pools seems very strange to me when a simple application of 10lbs of di-chlor would be so much more convenient and effective. A rise of 9ppm or even 20ppm in cya has virtually no effect on sanitation and would not affect their pools in any way. It will after all need to be replenished at some point anyway. Yet to avoid it they will go buy cases of clorox and lug literally hundreds of lbs of liquids around. I don't get it.

    All of the cya problems I've seen in my pools have been from little or no cya. I can't say I've ever told a customer "I'm sorry your pool is green ma'am it's gotta be the stabilizer, the cya levels are too high!" I'm sorry people but in my experience cya does not turn your pool green.
    I understand that at some point too much can be a problem, but jeez guys if you have to shock your scg pool 2 or 3 times a year it's not going to hurt to use one ten lb. bucket of di-chlor and it will be much easier and more effective than 17 gallons of bleach. to avoid

    For the record I do not sell Chlorine, I run a pool service and repair company and am responsible for the maintenance of a large number (you would be surprised) of residential pools.
    I see your point, I think. However, if a poster comes on with algae in their pool, and they reveal their CYA is say 151, you can bet I'm not gonna recommend they use Dichlor to shock their pool. The only time I would recommend someone use dichlor to shock is if their CYA is below the recommended range and they need to raise it, and they just happen to have some dichlor on hand.
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: CYA from 60 to 0 ppm

    We constantly get people coming to TFP because they can't get rid of algae and the cause very frequently turns out to be too high a CYA level from using stabilized chlorine. Often they have spent several weeks and huge quantities of chlorine, and often algaecide as well, to no effect. Once they start following our advice and lower the CYA level the pool is normally all cleared up in a week.

    Adding say 30 ppm of FC, about what it might take to fight a major algae bloom, from dichlor adds 27 ppm of CYA. Raising CYA by 27 is not always a problem but is often enough to start causing trouble, depending on your starting CYA level. If you combine that with trichlor usage it is almost sure to result in problems before the end of the season.
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    Re: DiChlor vs Bleach

    I can tell you from my own personal experience using Trichlor tabs over just one and a half seasons at a very low chlorine demand at less than 1 ppm FC per day that high CYA levels are a problem. I got to 150 ppm CYA and couldn't keep up with chlorine demand as algae (not yet visible, but water was a little dull) started to grow faster than chlorine could kill it and I was using PolyQuat 60 though only every other week. I have a cartridge filter so no backwashing. In pools with lots of dilution, that's one thing, but in situations such as mine getting to high CYA is just too easy when using stabilized chlorine products.

    I can also attest to algae growing when the FC/CYA ratio gets somewhat below 5% since 2 ppm FC when I had 50 ppm CYA would start to get some algae growth (water turning dull and higher chlorine usage). Also, these levels of FC and CYA were originally determined by Ben Powell who started The Pool Forum and Pool Solutions based on his experience of pools he serviced. And as Jason has said and if you look on this and other pool forums, virtually every single case of algae growth is from an FC/CYA ratio that is too low, not just an FC that is too low by itself (though that is also common). There are many SWG pools with 1-2 ppm FC (and a few with 3 ppm FC) and 70-80 ppm CYA that get algae whereas after they shock and then set a target of 4 ppm FC, they do not.

    Now as far as bacterial kill times, that's not something you would readily see in your pools and besides, bacteria are incredibly easy to kill for the most part. It takes a lot higher chlorine level to prevent algae growth than to kill bacteria or inactivate viruses. Nevertheless, 1 ppm FC with 100 ppm CYA results in slower 10-20 minute 99% kill times so might be an issue for person-to-person transmission though would not be an issue in terms of uncontrolled bacterial growth. For example, see Figure 4 for a kill time graph in this document which states in its abstract:

    Concentrations of 25, 50, and 100 mg of the chlorine stabilizer cyanuric acid per liter increased the time required for a 99% kill of Streptococcus faecalis by 0.5 mg of chlorine per liter at pH 7.4 and 20 C from less than 0.25 min without cyanuric acid to 4, 6, and 12 min, respectively.

    In fact, the 99% kill time with no CYA is 7-10 seconds since the 6-log 99.9999% kill time as specified for 1 ppm FC of chlorine in the EPA DIS/TSS-12 standard is less than 30 seconds. If you want me to link you to the many other studies measuring bacterial, virus, protozoan kill/inactivation times as a function of chlorine level with and without CYA, I can do that, but again that's not the reason we are focussed on CYA in this forum -- it's to prevent algae growth using chlorine alone. You can look at a large study I analyzed from Pinellas County here, but that just shows that bacteria are so easy to kill that it's hard to see whether FC alone or the hypochlorous acid concentration is the primary factor. It's mostly lab studies under carefully controlled conditions that show that it is the hypochlorous acid concentration that matters and not FC alone in terms of sanitation (for algae growth, we have thousands of multiple forum users to attest to prevention via paying attention to FC/CYA). For example, see this link that states the following with regard to inactivation of one species of protozoan cyst:

    The results strongly suggest that HOCl is the predominant cysticide with no measurable cysticidal effect of the chlorinated cyanurate species.

    The "chlorinated cyanurate species" is chlorine bound to CYA and most of the chlorine is bound to CYA (that comes directly from the chemical equilibrium constants) while "HOCl" is hypochlorous acid. If you believe that ORP measures anything significant, then you can see from the following two graphs that ORP is not correlated with FC alone but rather to hypochlorous acid concentration (and this is reasonably approximated by the ratio of FC to CYA though this isn't shown in the graph, but I linked you to the derivation of the approximation and you can validate that it's the case using my spreadsheet to calculate hypochlorous acid concentraton).





    The above was taken from 620 samples from 194 pools and spas with the data collected by Jeff Luedeman in Bloomington and Richfield, Minnesota. I didn't have some newer temperature dependence on some of the equations that I found out later, but this won't change the results very much. There's a lot of scatter and outliers (a small amount of variation is from the different pH), but the basic trend is pretty obvious. In the lower graph, the diamonds to the upper right are unstabilized pools, the diamonds to the lower left are stabilized pools, and the squares with the red borders are stabilized pools with CYA < 30 so 15 ppm was used in the calculations. (The first graph says "DPD" for the Free Chlorine axis, but in fact a FAS-DPD test from the Taylor K-2006C kit was used).

    [EDIT] In the above study, comparing ORP readings from a portable Oakton ORP measuring device vs. the built-in ORP controllers in many of the pools, 30 out of 130 (23% of those that had built-in ORP controllers) were off by more than 100 mV. [END-EDIT]

    If you wanted a more concentrated source of chlorine to use to avoid carrying around heavier bleach or chlorinating liquid, then why not use Cal-Hypo instead? It raises CH, but in percentage terms the effect is far less since for 10 ppm FC it's 7 ppm CH out of perhaps 300 ppm (2%) compared to Dichlor which is 9 ppm CYA out of perhaps 70 ppm (13%). Or if price is no object, then you can use lithium hypochlorite which won't add to either CYA nor CH.

    Richard
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    Re: DiChlor vs Bleach

    I will start checking cya more often to see if any patterns develop. I respect your opinions and am always looking for another tool to put in my toolbox, so to speak.

    To date I have never had a problem (with a residential pool) that was solved by reducing cya levels. You can tell people whatever you want about their water samples but I've been in their yards and worked on their pools. The vast majority of my service calls on algae are due to inadequate chlorine/ph levels, inadequate filtration or just plain lack of maintenance. Once I or my techs get that sorted out they always clear right up. So telling a random person who may or may not have a clue that their pump impeller is clogged or that doesn't know to add DE to their DE filter that they have a high cya level is pretty useless. Something to check? Sure, but there are 1,000,000 other things (don't ask me to name them) that I would be checking before I chalked an algae problem up to high cya.
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    Re: DiChlor vs Bleach

    Just to be clear, it's not high CYA by itself that is the problem or "causes algae". It's the FC/CYA ratio getting too low that lets algae grow faster than hypochlorous acid can kill it. And even then it doesn't mean algae will form since low phosphates or nitrates or inadequate (or too much) sun exposure can reduce or prevent algae growth, as can the use of supplemental algaecides.

    What would be most useful for us is for your techs to note for every case of algae growth what the FC, CYA and pH levels were just before the algae growth started. Obviously after algae starts to grow, the FC will tend to get too low so you won't be able to know what happened unless you knew the reading before the FC dropped. I'm sure that many pools with low CYA levels will also get algae because the FC got close to zero (perhaps because the CYA was too low so sunlight depleted the FC too quickly). Also, if you know the typical FC level that is maintained in your higher (> 60 ppm) CYA pools, then that will be useful info. There was one pool service manager who also said that CYA wasn't an issue even up to 100 ppm, but when asked he wrote he always had the FC levels in such pools at 4-6 ppm and sometimes had a couple of pools get algae to which he shocked and if the algae came back again he used a phosphate remover (so this wasn't a surprise to me).

    Richard
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    Re: DiChlor vs Bleach

    Like I said I have read the articles in AQUA and Pool and Spa News so I understand the concept, I've just never seen it happen. Likely due to the fact that my pools are maintained at ~3-5ppm instead of the 1-3ppm. I even tell customers to keep it there to avoid another service call.
    I will keep this in mind as these types siuations arise. I guess it's just easier to add a little more chlorine than to mantain lower cya levels. Are there any problems with keeping cl at 3-5ppm as opposed to 1-3ppm other than added cost?
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    Re: CYA from 60 to 0 ppm

    Quote Originally Posted by chem geek
    Quote Originally Posted by kiksroks
    So say I've got 0 fc in my scg pool (due to heaver bather load, dirty cell, space wolves, whatever) and the cya is at 80 ppm (max recommended by scg manufacturers) and I add enough di-chlor to get 10ppm fc; What effect would the additional 9ppm of cya have on my pool.

    The last time I saw space wolves there was Wild Turkey present as well!
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    Re: DiChlor vs Bleach

    Quote Originally Posted by kiksroks
    I guess it's just easier to add a little more chlorine than to mantain lower cya levels. Are there any problems with keeping cl at 3-5ppm as opposed to 1-3ppm other than added cost?
    Nope, it's not a problem having a higher FC level when the CYA level is higher. The only problem is that IF one gets algae starting to form, then it takes a lot more chlorine to get ahead of it if the CYA is higher. So you just have to be more diligent, that's all. The only other issue with a high FC high CYA pool is that you don't want to drink lots of the water, but that's not something you do anyway. In a commercial/public pool situation, it's virtually impossible to shock a pool to inactivate Cryptosporidium if the CYA level is high as you need to shock to an FC up to 10 ppm higher than the CYA level for 25 hours (to have an effective FC equivalent of 10 ppm if no CYA were present). So 30 ppm CYA is usually the most for such pools, but then again the bather loads are typically so high that any more CYA isn't worth it anyway since the loss of chlorine from bather load is quite a bit larger than that lost from sunlight at that CYA level.

    If one does want to operate at a higher CYA and not have the FC be higher, then a supplemental algaecide can be used. This is perfectly reasonable, it just costs more but is more convenient and provides "insurance" if the FC drops too low between chlorine dosing.

    There is a pool service called Pool Chlor that uses chlorine gas and chlorinating liquid and services pools once a week in very hot areas with intense sun. They have the CYA in such pools at 100 ppm and get the FC to 14 ppm and then it drops to around 4 ppm the next week when they add more chlorine. They service thousands of pools and have virtually none of them get algae unless someone forgets to add chlorine or is delayed in doing so. None of their customers complains about any stinging or other effects from the high FC -- mostly because 14 ppm FC with 100 ppm CYA is technically equivalent in chlorine "power" to about 4 ppm FC with 30 ppm CYA or to 0.14 ppm FC with no CYA.

    My wife uses a community center indoor pool over 5 months of the winter season that has 2 ppm FC with no CYA and we have to replace her winter swimsuits every season because the elasticity wears out (they also show first signs of fading) and her skin gets flaky and hair frizzy so she has to use extra products to take care of that. In our own pool during the 7-month summer season that has 3-5 ppm FC with 30 ppm CYA, her summer swimsuits have lasted for many years with minimal signs of wear and her skin and hair aren't affected very much. The difference, I believe, is due to the factor of 20 difference between the amount of "active" chlorine in the indoor pool and our outdoor pool.

    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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    Re: DiChlor vs Bleach

    It sounded like I was being quoted absolute truths there for a minute

    Like PoolChlor my company services alot residential pools once per week with natural water temps approaching or exceeding 90*f and we do it with di-chlor so I'm sure some of our cyas are way high. We try to have 3-5ppm fc when we get back the following week. Very few of our pools are anything but sparkling clear but when problems do present themselves we will use algaecides and phosphate removers as required to remedy the situation.
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    Re: DiChlor vs Bleach

    So your residential pool situation makes sense since the FC level doesn't get too low -- you must service in a less sunny environment unless you get the FC really high to have it last the week. Even if the FC is a little on the low side by the end of the week, you're raising it high so that it will last and this will kill off any nascent (not yet visible) algae that started to grow. It's the commercial pool situation you mentioned here that doesn't make as much sense unless your water is somehow naturally algaestatic.

    By the way, my pool is normally 86-90 in temp and it has 2000-3000 ppb phosphates. Our fill water is around 300-500 ppb phosphates (they are used as a corrosion inhibitor). Perhaps that is a difference between some of these situations -- maybe the bigger problems are in parts of the country where phosphates are used in the water system or blown in more from fertilizers (and dirt). Chlorine alone can manage this, but certainly with some waters lower chlorine levels relative to CYA are just fine. Do you mind telling me the general area where the pools you service are located? Do you know the phosphate and nitrate levels in your pools and/or fill water (usually there are minimal nitrates in fill water as its EPA regulated)?

    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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    Re: DiChlor vs Bleach

    [quote="kiksroks"]I will start checking cya more often to see if any patterns develop. I respect your opinions and am always looking for another tool to put in my toolbox, so to speak. [quote]

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