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Thread: rising ph levels

  1. #1
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    Default rising ph levels

    Why does my ph keep rising?

    Latest readings:
    tc 2.5
    fc 2.5
    cc 0
    cya 40
    alk 150
    ph 7.8

    intex above ground 18x48

    Yesterday all readings were the same except ph was 7.5

    It took us a long time adding muractic acid and then aerating to get the alk down, but now the ph keeps rising. We will add acid and it will drop to 7.2 to 7.5, but a couple of days later it will be up to 8. What do I need to do?

  2. #2
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    Default Re: rising ph levels

    I think that the alk is still a bit high, and also if you have kids who use the pool, then with splashing and all it will raise the Ph. Are you still aerating, that will raise the Ph also. I have found that adding acid to my pool around once a week is necessary as the Ph does seem to rise a bit, although slowly. If I am not mistaken the Alk needs to be at the highest 120, but I could be wrong.

  3. #3
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    Default Re: rising ph levels

    I'm still experimenting with this, so take that as a note of caution.

    I lowered the alkalinity in our pool from 220ppm to 100ppm and still had the pH bounce back up to 7.6 each day after adding muriatic acid the day before to get it down to 7.2. So I lowered the alkalinity to 70-80ppm and now the pH is holding at 7.2 over the last two days. Be careful with the amount of acid added as you approach the lower alkalinity levels, a little has a bigger effect on the pH and it doesn't bounce back as far.

    I'm not sure of the chemistry involved, but I suspect there's a CO2 interaction ocurring at the water surface/atmosphere interface that sets the pH dependent on the alkalinity.

  4. #4
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    Smile Re: rising ph levels

    The pool is vinyl lined and I thought my alk levels were okay for my pool. I stopped aerating after I got the alk down and there really hasn't been anyone in the pool. I guess you just have to keep adding acid to keep the ph down. Thanks for the help.

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    Default Re: rising ph levels

    What does the check mark after my post mean? Just curious.

  6. #6
    SoCalBoo is offline Registered+ Thread Analyst SoCalBoo 0
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    Default Re: rising ph levels

    wolfcue - you don't have an swg by chance, do you?

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    Default Re: rising ph levels

    Quote Originally Posted by wolfcue
    What does the check mark after my post mean? Just curious.
    It means you are subscribed to the thread and you can check settings in your control panel to get email notifications of new posts in the thread.
    Retired pool store and commercial pool maintenance guy.

  8. #8
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    Default Re: rising ph levels

    Rising pH
    Are you using the all bleach method? If you are, that may be why it is climbing.
    Anything that you add to the pool, can change the pH depending on the pH of what you are adding.

    Bleach, sodium hypochlorite, has a pH of around 10 or 11, very alkalotic, so the more you add, the higher your pH will go.
    I have found that in my pool which is open all year round, I ONLY ADD 2 chemicals!!!!!!!!

    Bleach and Acid.
    Bleach for my source of chlorine and acid once in a while to bring the pH down.
    That is it. Once your pool is "tuned" it can be that simple.

  9. #9
    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: rising ph levels

    Quote Originally Posted by azimmer1
    Rising pH
    Are you using the all bleach method? If you are, that may be why it is climbing.
    Anything that you add to the pool, can change the pH depending on the pH of what you are adding.

    Bleach, sodium hypochlorite, has a pH of around 10 or 11, very alkalotic, so the more you add, the higher your pH will go.
    Though you are correct that bleach is alkaline (the 12% stuff from pool stores has an even higher pH of 13), chlorine usage is an acidic process so the net effect of chlorine addition and usage is a very small rise in pH due to the extra base that is added to (or kept in) the chlorine bleach (to keep it more stable). When chlorine is broken down by sunlight (UV) or consumed by ammonia to breakpoint or oxidizing organics, the pH goes down by almost the same amount as it goes up when you added it.

    [EDIT]
    By "chlorine usage" I mean when chlorine gets "used up", not your usage (addition) of chlorine. Sorry for the confusion.
    [END-EDIT]

    After reading several posts about pH rise, I am coming to the conclusion that it is most often due to outgassing of CO2 which raises pH (and when you add acid to compensate, the alkalinity is lowered and you get back to the original pH -- so the net change of CO2 outgassing plus adding acid is that the alkalinity drops). Aeration of pool water is the most common cause for this. It looks like many people live with a lower alkalinity of around 80 in such environments. Also, keeping your pH closer to 7.5 helps since lower pH accelerates the outgassing process.

    Richard
    Last edited by chem geek; 07-19-2006 at 09:28 PM. Reason: Clarified "chlorine usage"

  10. #10
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    Default Re: rising ph levels

    Thanks to everyone for the help.

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