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Thread: 1) How to lower pH when alkalinity is low and 2) maintenance FC levels

  1. Back To Top    #1

    Join Date
    May 2015
    Hamilton, NJ

    1) How to lower pH when alkalinity is low and 2) maintenance FC levels

    It took a while to get our water balanced for which I can only credit the amazing support of TFP experts and members and some sleepless nights on our part. We have enjoyed sparkling water with all the chemistry in balance since the end of June. I now have two questions:

    1) The pH is slowly rising (now at 7.8 or maybe a bit more) while the alkalinity is on the low side. From what I read, I should adjust to a pH of 7.5, but this will bring the alkalinity down even further. How do I go about decreasing pH without affecting alkalinity too much? I know that you can aerate to bring pH up again after using muriatic acid, but I haven't read how you can increase alkalinity and not pH. Part of me is hesitant to start adjusting the chemicals because it was so hard to get the water balanced in the first place.

    2) We use liquid chlorine (12.5%) and add about 1.5 - 2 quarts a night to bring the FC up to 8. Because we have full sun for 12 hours a day, the FC goes down to about 5 - 5.5 by the next evening. Our CYA is approximately 40 which, according to the CYA/chlorine chart, means we're targeting a FC of 5 and a minimum of 3. Are we overshooting and wasting chlorine? Should we only bring the FC up to 7 at night? Again, after our many prior problems, I've been afraid of hitting the minimum FC on a sunny day or just not trusting that our CYA readings are accurate as this test is subjective.

    We use the TF-100 kit and our readings today are:
    pH = 7.8 or a little higher
    Alkalinity = 80
    FC = 7.5
    CYA = 38 - 40
    Calcium Hardness = 425

    Thanks for any advice.
    Inground pool with vinyl liner, 22,500 gallons. DE filter.

  2. Back To Top    #2

    In the Industry

    Donldson's Avatar
    Join Date
    Jun 2009
    NW Ohio

    Re: 1) How to lower pH when alkalinity is low and 2) maintenance FC levels

    Sounds like you actually have things down pretty well and just a little fine tuning is needed.

    1) adjust your pH as needed. Your TA can go a bit lower if that will help keep your pH stable. I personally treat the recommended TA levels as guidelines rather than rules, as long as it doesn't bottom out you should be fine.

    2) you want to keep your FC so it doesn't drop below 3. It sounds like you can target 6-7 at night and will not drop below 3. Feel free to experiment with it to see what works best for your pool.

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