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Thread: where to add bleach?

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    Default where to add bleach?

    Just switched to BBB method. Is it better to add bleach to skimmer, or does everyone slowly pour in front of returns?

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    Default Re: where to add bleach?

    Quote Originally Posted by kjmelak
    Just switched to BBB method. Is it better to add bleach to skimmer, or does everyone slowly pour in front of returns?
    kgm ...

    From reading posts on this site, I believe you can do either UNLESS you have a automatic chlorinator ... then I would just slowly pour it in the deep end in front of a return.

    I belive there are some threads on this ...

    Also, have you already posted test #'s and do you know how MUCH bleach to add to the pool? You can download the bleach calculator -- VERY HELPFUL!

    Anyway, try to search for those threads ... and keep us posted!
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    Default Re: where to add bleach?

    Quote Originally Posted by kjmelak
    Just switched to BBB method. Is it better to add bleach to skimmer, or does everyone slowly pour in front of returns?
    Though the high pH (alkaline) of bleach isn't as bad as acidity, I would pour it slowly in front of the returns. It seems to mix rather quickly that way while still being briefly concentrated for a localized super-shock.

    One of these days if we understand why SWG systems are so effective, the recommendations for chlorine dispersal might change. For instance, I wouldn't be surprised if we find that it's more effective to add it with the pump off so that it slowly disperses giving plenty of contact time to oxidize the bad stuff you want destroyed in your pool (chloramines, chlorinated organics). Then, after a short time (15-30 minutes?) the pump would be turned on to make sure the residual gets everywhere. That's not a recommendation, just a future possibility. For now, stick with the returns.

    Richard

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    Default Re: where to add bleach?

    Quote Originally Posted by Watermom
    Either way is fine. In my pool, I just pour it in the skimmer while the pump is running.
    I know that the basic pH won't harm the copper pipes in the heater, but isn't it a potential problem for a cartridge filter or sand or DE? I don't know, I'm just speculating. If you pour the chlorine quickly into the skimmer, it will raise the pH quite a bit (if you poured at the rate of suction for perhaps a 50/50 mix, then the pH would be only a little less than the bleach pH itself -- pH is logarithmic and doesn't average).

    Richard
    Last edited by chem geek; 07-25-2006 at 10:56 PM. Reason: changed "rise" to "raise"

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    Default Re: where to add bleach?

    I don't think it would raise the PH as much as you think it would. It is logarithmic but negative of the PH so high PH has much less effect than low PH. I think bleach has a PH of arround 13 so for non-buffered solutions,

    PH = -log10(0.5*10^(-7.5)+0.5*10^(-13)) = 7.8

    With buffers as in pool water, it will not change even half of that.

    Had to add one more thing. This is the reason that acid works so well when lowering PH and why you don't want to add it to the skimmer. I think I read somewhere that 30% muriatic acid has a PH of -1. So a 50/50 mix would be:

    PH = -log10(0.5*10^(-7.5)+0.5*10^(1)) = -0.7

    Almost as bad a pure acid. Of course the buffers will resist a change but the PH will still be quite low.
    Last edited by mas985; 07-25-2006 at 11:06 PM.
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    Default Re: where to add bleach?

    Quote Originally Posted by mas985
    I don't think it would raise the PH as much as you think it would. It is logarithmic but negative of the PH so high PH has much less effect than low PH.
    You are absolute right. My bad. That's what happens when I think off the top of my head and don't do the math. Thanks for catching that!

    [EDIT]Hold on a moment...Now that I'm actually working it through, it isn't working out as you showed. Think about diluting Sodium Hydroxide by mixing it with half water to go from a 2 molar solution to a 1 molar solution. It doesn't take on the pH of the neutral distilled water. So hold on a moment while I try to sort this out.[END-EDIT]
    Last edited by chem geek; 07-25-2006 at 11:29 PM.

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    Default Re: where to add bleach?

    OK, I've got this figured out. You can't just look at a single species such as H+ when you are dealing with water because there is the equilibrium going on:

    ..... H2O <--> H+ + OH-

    With the equilibrium constant Kw=[H+][OH-]=10^(-14)

    Since H+ and OH- can get consumed into H2O, the easiest way to do the mass balance is to forcibly consume the smaller of the two components into H2O so that the quantity [H+]-[OH-] represents the excess H+ or if this is negative then this represents the excess OH-.

    Now when you mix the two solutions together, all you have to do is add the two "excesses" and you almost have your answer. This will tell you the rough extra amount of one species over the other, but then water will dissociate to fill in some more in order to get to equilibrium.

    So, when you add bleach, which is only about 11 pH or so (its liquid chlorine that's 13), we have the following:

    Pool solution of pH 7.5: [OH-]-[H+] = 10^(-14)/10^(-7.5) - 10^(-7.5) = 2.85x10^(-7) excess OH-
    Bleach: [OH-]-[H+] = 10^(-14)/10^(-11) - 10^(-11) = 10^(-3) excess OH-

    Adding the two together gives roughly the excess concentration of OH- over H+ of the Bleach or 10^(-3). A little water dissociates so that [OH-] is about 10^(-3) while [H+] becomes 10^(-11).

    Now you made a point about the buffer solution and you are correct that this will an effect except I believe the buffer gets overwhelmed with this amount of base. I have a spreadsheet with all the equations in it and when I mix an equal liquid volume of bleach with water I get a pH of 9.86 so my guess about the buffer being overwhelmed is correct.

    [EDIT]The way to think about what happened to the H+ in the pool when the two liquids were mixed is that the 10^(-7.5) concentration of H+ in the pool gets mixed with this very basic solution with all of this extra OH- hanging around so to maintain equilibrium most of this H+ combines with this newly introduced OH- and turns into water.[END-EDIT]

    Now a pH of 10 isn't awful. Putting in chlorinating liquid that starts at a pH of 13 would be much worse as it would result in a pH of about 12.5

    Anyway, I don't know that this pH is bad for the filter, I just was asking.

    Richard
    Last edited by chem geek; 07-25-2006 at 11:37 PM. Reason: added another "excess OH-" wording and some other incorrect wording

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    Default Re: where to add bleach?

    I don't agree with the idea that it's going to be a 1 to 1 ratio. My pump supposedly pumps 75 gpm at 50 feet of head. Even if it were only 60 gpm that's one gallon per second. Assuming you dump a 1/2 gallon in in 5 seconds that's 1 part bleach to 10 parts pool water before it hits my pump.

    My DE filter contains at least 20 gallons of water so obviously it's never going to see a concentration of more than 40 to 1 if I add a 1/2 gallon of bleach to the skimmer.

    Maybe if you dump a gallon of bleach quickly into a small above ground pool skimmer you could do some harm but you'd probably have to pour from something faster than a bleach bottle to do it.
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