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Thread: Calcium Hardness keeps rising

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    Calcium Hardness keeps rising

    My pool's calcium Hardness keeps rising and I can't figure out why.

    Today's test
    FC- 3.5
    CC - 0
    PH - 7.5
    TA - 80
    CH - 450-475
    CYA - 80

    On 9/25 CH was 270. On 10/11 CH was 390.

    I'm using the TF-100 kit and tested CH twice today with readings of 450 and 475.

    I have an auto-fill, but the tap water CH is only 125.

    Any ideas? Thanks, Scott
    Scott, Oklahoma
    10K gal above ground

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    polyvue's Avatar
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    Re: Calcium Hardness keeps rising

    Do you use a pool service? How do you shock the pool? How often in the past two months has it been shocked? I'm wondering whether you or someone else has been adding Calcium Hypochlorite in the form of shock powder or pucks, or possibly dumping Calcium Chloride in the water when you're not around. Whatever the source, you may want to think about doing a partial drain and fill (say 10-20%) to reduce it, especially if it continues to climb.
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
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    View of spiral galaxy in Ursa Major NGC6217 - Hubble Telescope 2009

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    Re: Calcium Hardness keeps rising

    I do all the work myself. I last shocked at the end of August. The only thing I have added in the last two months is MA (regularly), about 3 Lbs of baking soda, and about 4 lbs of CYA (99%). No one has been swimming much in the last month.

    I understand about draining/refilling, but I really want to figure out what is causing the rise so I don't have to keep dumping water.
    Scott, Oklahoma
    10K gal above ground

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    duraleigh's Avatar
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    Re: Calcium Hardness keeps rising

    To my knowledge, the only way you can increase CH in a pool is thru fill water (which you're not) or by adding it with the chemicals polyvue has mentioned (which you're not).

    I have no explanation.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Calcium Hardness keeps rising

    How old is the pool? Was it recently resurfaced?
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Calcium Hardness keeps rising

    Evaporation only takes up pure water, leaving the calcium that was in the pool behind. When you go to refill your pool to the proper water level, the 125 ppm of CH thats in the tap water is going into the pool. Its also possible, but unlikely, that the water is taking the CH out of the plaster itself.
    Gilbert, Arizona
    30,000 gallon IG Salt Water Pool

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    Re: Calcium Hardness keeps rising

    OP's posts indicate pool is not new.....but doesn't confirm that.

    For the amount of increase indicated, evaporation would have to be enormous.....in Sep and Oct......that doesn't seem likely.

    Unless this pool was put in late Summer, I am still at a loss.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Calcium Hardness keeps rising

    The other possibility, much as I don't like to suggest it, is testing error.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

  9. Back To Top    #9

    Re: Calcium Hardness keeps rising

    Pool was completed in June. I went to a local pool store that has been relatively good in the past and they measured CH at 320.

    Looks like I'm going to have to partial drain for other reasons as well so I will try that and continue to monitor.

    Thanks, Scott
    Scott, Oklahoma
    10K gal above ground

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