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Thread: A Theory About Rising pH in SWG Pools

  1. #51
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    Default Re: A Theory About Rising pH in SWG Pools

    Quote Originally Posted by klharmon View Post
    I go through about 1/2 gallon a week of muriatic acid on my 19,000 gal in ground pool, and I have an AquaPure 1400 SWG. I have a waterfall feature that I use rarely, so a majority of the time the pool just vacs & filters.

    pool is relatively new, plaster bottom, and I check pH twice a week.
    What's your TA, CYA and pH?

  2. #52
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    Default Re: A Theory About Rising pH in SWG Pools

    Quote Originally Posted by KurtV View Post
    Richard,
    Updated data. I think the acid demad might be letting up a bit.

    Date pH Alk. Acid addition
    7/26 7.8 100 24 oz.
    7/27 7.4 100
    7/28 7.8 100 16 oz.
    7/29 7.7 100 16 oz.
    7/30 7.2 90 32 oz. (before testing)
    7/31 Vacation
    8/1 Vacation 16 oz.
    8/2 Vacation
    8/3 Vacation 16 oz.
    8/4 7.8 90 28 oz.
    8/5 7.6 80 16 oz.
    8/6 7.6 80 16 oz.
    8/7 7.4 80 8 oz.
    8/8 7.6 70 16 oz.
    8/9 7.6 70 16 oz.
    8/10 7.5 70 16 oz.
    8/11 7.3 70 8 oz.
    8/12 7.4 70 16 oz.
    8/13 7.6 70 16 oz.
    8/14 Work trip
    8/15 7.6 70 16 oz.
    8/16 7.6 70 24 oz.
    8/17 7.4 [IMG]file:///C:/DOCUME%7E1/CLV/LOCALS%7E1/Temp/moz-screenshot-2.jpg[/IMG][IMG]file:///C:/DOCUME%7E1/CLV/LOCALS%7E1/Temp/moz-screenshot-3.jpg[/IMG]65 16 oz.
    8/18 7.4 60 8 oz.
    9/19 7.5 60 20 oz.
    8/20 7.2 60 8 oz.
    8/21 7.4 60 8 oz.
    On another pool forum (poolcenter.com) in this thread via an unfortunately not-so-nice discussion, I calculated whether the SWG produces enough hydrogen gas bubble volume to have the small amount of carbon dioxide that would be allowed into it (via Henry's Law for equilibrium) to make the pH rise. It isn't enough and that's under ideal conditions with full equilibrium reached (TxPool says the kinetics don't allow for any effective transfer, but I'm not sure about that -- in any event, the volume just isn't enough).

    So, I'm back to leaning towards the other explanation I originally started with in this post in this thread where I thought it might be undissolved chlorine gas bubbles. If this is the case, then one way to improve the situation could be to point the returns downward to give the bubbles a greater chance of dissolving more completely into the water. The lower TA effect that KurtV saw wasn't huge and could just be regular carbon dioxide outgassing without much change from the SWG itself -- that is, the SWG effect may mostly be chlorine gas escaping.

    KurtV (or anyone else with an SWG that would like to experiment), if you are still experiencing a rising pH in your SWG pool, can you try pointing the returns downward and seeing if that makes any difference? Can you see the bubbles at night to see if they linger longer when the returns point downwards or if you notice any of them getting smaller in the water (dissolving)? Do you ever smell any fresh chlorine smell over the return where the bubbles come up compared to other parts of the pool where there are no bubbles?

    If the chlorine outgassing is a primary cause for the incremental pH rise in SWG pools, then I would expect this effect to be worst in pools with short distances between the SWG and the pool returns and for 2-speed or variable speed pumps when the pump is on high speed but not on low speed. If pointing the returns downwards helps, then one has the trade off of rising pH vs. potentially worse cleaning of the pool water surface into the skimmer (which I think is better when the returns are not pointed downwards).

    Richard
    Last edited by chem geek; 06-23-2008 at 03:51 PM.

  3. #53
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    Default Re: A Theory About Rising pH in SWG Pools

    My pool has three returns, the third does not bubble at all, I will leave it pointing up and point the other two down. I have a cover, which I keep on most of the time when the pool is not in use and need to add 1Qt of acid a week. It will be interesting to see if this makes any difference. I guess it is finally time to start a log so I can figure out what really is going on versus my gut feel.

    Mark

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    Default Re: A Theory About Rising pH in SWG Pools

    Mark,

    That's REALLY interesting that one of your returns doesn't bubble at all. I assume all three are coming from the output of your SWG, right? You don't have any sort of bypass of flow with some going around your SWG to one return, right?

    If the SWG output is going to all three returns, then is the one return with no visible bubbles at a farther distance away from your SWG? If so, then the theory of the chlorine bubbles needing more time to dissolve may very well be on the right track.

    I would think that a pool cover would keep the chlorine in contact with the water longer so that it would eventually dissolve and not escape, but I suppose we'll find out.

    I'm looking forward to the results of your experiment. Thanks!

    Richard
    Last edited by chem geek; 06-25-2008 at 10:10 PM.

  5. #55
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    Default Re: A Theory About Rising pH in SWG Pools

    Yes, the first return is about 15 feet from the pool equipment, the second about 25 and the third about 40 feet away. My presumption has been that the bubbles all escaped at the earlier ports, but it could be absorption. I will ask some family members to also give the area where the bubbles surface a sniff to see if they can smell chlorine. Many of the tiny bubbles remain in suspension, never surfacing. I can wipe them off of any surface underwater with my hands, including the cleaner hose which is 20 feet from the nearest return.

    There is no bypass of any kind. I have only a single speed pump and the flow rate is pretty substantial.

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    Default Re: A Theory About Rising pH in SWG Pools

    All my returns, 1 - do not bubble, at least that I can tell, 2 - are pointed down because my cleaner instructions said to do that. I still take 3 pints (30K gallon plaster inground) every week.

    Just an F.Y.I.

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    Default Re: A Theory About Rising pH in SWG Pools

    Thanks. This is just one of those areas with multiple factors. Lowering TA does help, but doesn't always help that much.

    Not having any bubbles at all doesn't make that much sense since there should at least be hydrogen gas bubbles since I would expect the water to get close to fully saturated and for the hydrogen bubbles to outgas -- at least by the end of the day with the SWG still running. You might take a look at night with an interior pool light turned on (and, obviously, turning on the pump and SWG). Many times people don't see bubbles during the day, but can readily see them at night.

    Richard

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    Default Re: A Theory About Rising pH in SWG Pools

    I'll have to keep thought in mind as I can't see squat right now thanks to Hurricane Ike and no power. If I ever get back in (running out of season now) I'll post back.

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