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Thread: Safe swimming with elevated chlorine

  1. #41
    chem geek is offline PF Supporter Whibble Konker chem geek 4 stars chem geek 4 stars chem geek 4 stars chem geek 4 stars
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    Lightbulb Re: Safe swimming with elevated chlorine

    Carl,

    To keep my message short, I didn't give all of the details. With the following conditions:

    pH: 7.5
    FC: 3.0
    CYA: 30
    The following don't have a much smaller effect on HOCl:
    Temp: 80ºF
    TDS: 550
    The following has no effect on HOCl:
    CH: 300

    You get 0.045 ppm HOCl and 0.048 ppm OCl for a total of 0.093 or about 0.1 ppm total for HOCl and OCl-.

    I have been in communication with Ben on the detailed spreadsheet I created and plan to start a thread in the China Shop (perhaps this weekend) to start the discussion on getting real-world experiences from people. Though I am confident of the chemistry determining HOCl levels at various levels of CYA and FC and am also fairly confident of the 0.011 ppm HOCl level that is the minimum for disinfection (of easy bugs, not hard-to-kill ones), I am not at all sure what the proper levels of chlorine are needed to prevent algae nor to properly shock algae (and will likely vary by type of algae). This is where some real-world experience could help determine these values.

    The spreadsheet is complicated and solves the chlorinated cyanurate equations iteratively since an exact solution requires solving a quartic equation (or ignoring a very minor species, a cubic equation) and even then you need to iterate to solve for the ionic strength influences on activity. Nevertheless, there is an approximate formula you can use so long as your CYA ppm is at least 5 times your FC (the formula really falls apart terribly below a ratio of CYA/FC of 3).

    (ppm HOCl) = (ppm FC) / ( 2.7*(ppm CYA) - 6.6*(ppm FC) + 5.2 )

    and if you are interested in the FC for a given HOCl (to construct the equivalent of Ben's table, for example), you can use the following which just solves for ppm FC from the above.

    (ppm FC) = ( 2.7*(ppm CYA) + 5.2 ) / ( 6.6 + 1/(ppm HOCl) )

    The constants in the above formulas are for a pH of 7.5 (which is the only parameter that significantly affects these constants). With the spreadsheet I can easily calculate the constants for other pH, but remember that the above formulas are approximate. For example, with FC of 3 and CYA of 15 the formula gives HOCl as 0.117 when the correct answer is 0.107. That's not bad (about a 10% error). However, with FC of 5 and CYA of 15 the formula gives HOCl as 0.400 while the correct answer is 0.246 (about a 60% error) which isn't very good.

    Richard

  2. #42
    VOLDADDY is offline Lifetime Member Weir Watcher VOLDADDY 1 star
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    Default Re: Safe swimming with elevated chlorine

    Wow, the above post might as well have been written in Chinese to me, and I suspect 90% of the others here. We really appreciate all of the work people like Ben, Carl, Richard, Al, Janet, Michael and the bleach calc, et al...put in to this board, and breaking it down to laymans terms for everyone else to understand. Now I see why I didn't take chemistry in college, Biology and the 3 hour lab was enough for me. Kudos from everyone for all the work you guys and gals do. Too bad we all don't live near each other, or we could have a huge cook out and grill up some steaks to show our appreciation! (medium rare, of course )

  3. #43
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    waterbear is offline Lifetime Member Sniggle Mechanic waterbear 4 stars waterbear 4 stars waterbear 4 stars waterbear 4 stars
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    Default Re: Safe swimming with elevated chlorine

    Quote Originally Posted by PoolDoc

    Waterbear, this winter ask me for some of the bromine literature I have.

    I, for one, am not convinced that bromine has any real value for either pools or spas. And, I'm almost convinced that the use of BCDMH or any other source of bromine bound to dimethyl hydantoin should be strongly discouraged.
    Ben, on this I agree with you 100%. I have never understood the need for bromine tablets in a floater since they are not effective unless the bromine bank is first established with sodium bromine and converted to hypobromous acid with an oxidizer such as chlorine. My feeling is that they are totally unnecessary since bromine sanitation can be carried out with only the sodium bromide and oxidizer.
    I very strongly suspect that bromine has gained its positive reputation purely based on the absence of information. My impression is that chlorine and its compounds are far better known and understood than are bromine and its compounds. It's also my impression that bromates, which form under many conditions if bromine is used in pools or appears in source water, is considered a more serious 'bad actor' than are many of the chlorine products.
    I have read some vague things alone these lines but have not been able to find out very much info at all.
    Regarding bromamines, I've never been able to find *any* information on what sort of bromamines appear in pools and spas, nor have I ever found a study that substantiates the oft-repeated pool industry maxim that "bromamines, unlike chloramines are good sanitizers".
    Neither have I.
    It's worth noting, that with the demise of Hydrotech (purchased by BioLab), and the death of Jock Hamilton (founder of United Chemicals), pro-bromine pool industry press seems to have diminished to a bare trickle. It makes me wonder if ANYONE, except those trying to sell it, ever thought it was a good idea.

    Color me skeptical!
    Bromine's often quoted advantage is that it is active over a wider pH range (up to 8.0) and is more stable at higher temperatures but I have not been able to find any actual info to support this. Also bromine is a known sensitizer and reactions to bromine santized pools and spas is not uncommen. It is intersting that what I have read (in a CPO training manual) on the other halogens and why they are not applicable to pool sanitation are that flourine is too expensive although it would be extremely effective (although I personally believe it would also be very toxic) and that iodine in concentrations high enough to sanitize would color the water and would still need chorine present as an oxidizer. I have not been able to find any info to either prove or refute these statements. It makes me wonder where the 'experts' get this information from!
    Ben
    Color me skeptical too!
    Retired pool store and commercial pool maintenance guy.

  4. #44
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    Default Re: Safe swimming with elevated chlorine

    Quote Originally Posted by chem geek
    pH: 7.5
    FC: 3.0
    CYA: 30
    The following don't have a much smaller effect on HOCl:
    Temp: 80ºF
    TDS: 550
    The following has no effect on HOCl:
    CH: 300
    Richard,

    What effect, though small, does TDS have on HOCl? Would the fact that salt makes up the majority of TDS in a particular sample increase the negative effect? Go easy on my limited abilty to grasp basic chemistry .

    Dave

  5. #45
    chem geek is offline PF Supporter Whibble Konker chem geek 4 stars chem geek 4 stars chem geek 4 stars chem geek 4 stars
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    Default Re: Safe swimming with elevated chlorine

    Quote Originally Posted by DavidD
    Richard,

    What effect, though small, does TDS have on HOCl? Would the fact that salt makes up the majority of TDS in a particular sample increase the negative effect? Go easy on my limited abilty to grasp basic chemistry .

    Dave
    In the presence of even small amounts of Cyanuric Acid (CYA), TDS has almost no effect on HOCl. So the calculations for a salt (SWG) pool would be the same as for a regular non-salt pool.

    In a pool with no CYA, then the HOCl concentration from a non-salt pool to a salt (SWG) pool is lowered by around 5.7% (independent of Total Free Chlorine (FC) level).

    Stop reading at this point. The following is for those who might want a more technical explanation.

    (The technical reason for the difference is that without CYA, the TDS affects something called "ionic strength" that affects the equilibrium between the neutral HOCl and the charged OCl-. With CYA, the concentration of HOCl is instead determined by the CYA-like equilibrium that has charged species on both sides of the equation so the ionic strength effect is cancelled out. )

  6. #46
    fcfrey is offline ** No working email address ** Thread Analyst fcfrey 0
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    Thumbs up Re: Safe swimming with elevated chlorine

    So ---- What have we learned??

    After nearly two months, 90438 Characters (with spaces), making up 15683 Words, in 45 posts from 12 different contributors including our Administrator and Moderators, we have had a very spirited debate. We went over, under, around and some, directly to the question, which in case we have forgotten, “Is it safe to swim with an elevated chlorine level?”

    1. We have explored the politics, the fears, the fear mongers in the “Greenie” gang, and the chemistry behind effective chlorination.

    2. We’ve also discussed the way our mainstream media runs off with half of the story and creates the rest itself, true or not, to “sell papers”. Ben has very accurately pointed out the fact that “the fears that people bring to the Pool Forum are not, for the most part, irrational fears. Rather they are a rational response to the persistent and hyped anti-chlorine hysteria shrieked out by modern environmentalists and uncritically parroted by the mass media”. The latter being one of the most profound statements of the entire thread.

    3. We have learned that there are many forms of disinfection available for our pools including sunlight, UV, peroxide, bromine etc. etc., but none do the job as effectively as chlorine.

    4. We have learned that the real dangers are from the disinfection by products (DBPs) and Tri-Halo-Methanes (THM) particularly in indoor pool environments, but these problems really do not apply to our outdoor residential pools where there is plenty of ventilation. In addition the fear of chlorine being directly absorbed through the skin has been largely debunked, but there is evidence that some halogenated compounds -- that may, or may not be present in pools -- can be so absorbed. We should, however, keep in mind that these compounds are found in pools in many forms including salt and the very liners that keep the water where it belongs (in the pool).

    5. We’ve discussed lighting and algae formation in aquariums and the relationships to disinfection and sanitation.

    6. We even discussed DDT.

    7. We have learned that there are some members of this forum that are overly sensitive to what other members quote and are willing to lash out with concealed retribution, leaving the recipients with their “feel bad” hurt.

    8. We have learned that there is a need for compassion for the “unlearned” and those skeptical of the principles and practices taught here.

    9. And finally, we have gone --- w-a—y off topic to explore the area under CarlD’s bed

    But what about the question-----------------?????

    I think it is safe to say, “that all depends”. It depends on who is doing the tests, and are they accurate. It depends on how high your cyanuric acid level is. It depends on the level of your chloramines (combined chlorine). It depends on every other chemical we put into the pool. It depends on the environment in which your pool exists. But it really depends on how comfortable you are with what the administrators, moderators and other contributors on this forum believe.

    For me --- nearly two months after posting the question, and reading another 1000 or more posts on a lot of related subjects, I will now swim in my pool whenever it is 10 ppm free chlorine or less. I’m comfortable with that decision, a decision that I probably would not have been able to make without the debate that my question has brought forth.

    I’ve added another 656 words to this thread so I need to bring it to a close.

    Lastly --- I feel compelled to thank Ben, for providing this forum. Richard, for his detailed chemical explanations and charts. The Moderators who keep things going forward with their great advise. And finally all the newbies, some of whom ask some of the most ridiculous questions (sometimes they make me laugh) which bring out the very best information money could never buy.

    Frank
    Last edited by fcfrey; 06-29-2007 at 06:11 PM.

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