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Thread: Lowering alkalinity in Fiberglass pool

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    Lowering alkalinity in Fiberglass pool

    I have a Public swimming pool that has a TA of 180. This high alkalinity isn't causing any problems with the PH or the pool in general. However the state inspector will be coming by sometime this summer and he will want the alk at 120. I don't want to add muriatic acid because the pool is fiberglass and also because i don't want to lower the PH too much and have to shut down the pool. Any ideas on how to slowly lower the alk?

    I am adding 2 tri-chlor tabs a day to sanitize the pool. This also keeps the CYA at around 100ppm, because daily backwashing. I also add 1/2 cup soda ash daily. Thanks for any help

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    Join Date
    Feb 2008
    Denton, TX

    Re: Lowering alkalinity in Fiberglass pool

    Follow this process to lower TA...pool-school/lowering%20total%20alkalinity

    Muriatic acid is perfectly safe to use in a fiberglass pool, or any other surface pool for that matter, as long as you add it slowly by pouring it in front of a return with the pump circulating the water. Where people run into problems with acid or other pool chemicals is when they are allow to pool on the bottom of the pool with the pump off.

    With a CYA of 100, you need a minimum of 7 on your FC in order to kill pathogens and keep algae from growing in the water. It might be advantageous to change out some water and get that CYA down to a more manageable level.

    Not sure why you are adding soda ash to your pool, but by doing so, you are raising your pH and your TA every time you add it. If you want your TA down, you're going to need to stop adding soda ash.

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    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    SouthWest Alabama

    Re: Lowering alkalinity in Fiberglass pool

    In addition to what 257 said, Most CYA tests only test to 100 ppm and report everything above 100 as 100.
    How are you testing CYA?
    Are you sure your CYA is 100?
    I agree that most likely some draining is in order.
    Dave J. TFP Moderator
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    Re: Lowering alkalinity in Fiberglass pool

    My CYA is at 100. I use a CYA test kit from Rainbow pool products. The inspector wants the CYA at 100 so it has to be there which is why we use tablets. I use soda ash to raise the PH because the acidic tablets are bringing it down. Is there something better to use to raise ph without raising alk?

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Lowering alkalinity in Fiberglass pool

    You can use borax, sodium tetraborate decahydrate, to raise the PH and it won't raise TA as much as soda ash, but it will still raise TA a little. Another approach is to aerate the pool, presumably only when it is closed. Aeration will raise the PH without affecting the TA.

    Quote Originally Posted by keene3b07
    The inspector wants the CYA at 100
    That is insane. Where are you located?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Lowering alkalinity in Fiberglass pool

    Thanks. I am in socal it gets to be about 110 here in the summer

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