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Thread: What causes CH to rise?

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    phalcon51's Avatar
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    What causes CH to rise?

    Hi all,

    I'm having a problem with high CH levels and I'm wondering what causes it to rise over time. The level was at 250 ppm in early January, 2011 and then started rising in mid-March. Between April, 2011 and June, 2012 it rose from 270 ppm to 575 ppm. It's now up to 675 ppm and I'm in the process today of draining and replacing a large portion of the pool water. The CH of my fill water is 160 ppm.

    So, my question is, how can I prevent this from happening in the future? I've been using the BBB method (without any Borax yet) and the Pool Calculator set to TFP Goals since the pool was first filled after re-plastering in September, 2010. Could the curing plaster have contributed to the increasing CH levels? We are running an SWCG but I need to add bleach in the winter months when the water temp drops.

    Here are the results from the latest test (Using Taylor Complete FAS-DPD test kit from Leslie's)

    Pool Volume - 26,200 gal.

    FC - 3.5
    PH - 7.5
    TA - 60
    CH - 675
    CYA - 60
    Salt - 3800
    Temp - 50f

    Any help or advice appreciated.

    Gary
    26,200 gal. 35' x 16' Plaster IGP (50 yrs. old), Hayward 48 sq. ft. DE filter, Hayward EcoStar VS pump, Intellichlor IC-40 SWCG, The Pool Cleaner 4X suction, Pool Skim and Pool Devil skimmers. Re-plastered Sept. 2010.

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    duraleigh's Avatar
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    Re: What causes CH to rise?

    1. Even if your fill water is low in CH, CH will continue to rise through refill and evaporation.....you add more when you refill but it doesn't come out when it evaporates.


    2. The only solution is to do a partial drain and refill


    3. What is the CH of your fill water?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    phalcon51's Avatar
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    Re: What causes CH to rise?

    As noted in my original post, fill water CH is 160 ppm. Is it ok to just leave it at that level and let it rise on it's own, or is that too low? What's the minimum CH I can get away with for semi long-term use?

    Gary
    26,200 gal. 35' x 16' Plaster IGP (50 yrs. old), Hayward 48 sq. ft. DE filter, Hayward EcoStar VS pump, Intellichlor IC-40 SWCG, The Pool Cleaner 4X suction, Pool Skim and Pool Devil skimmers. Re-plastered Sept. 2010.

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    Richard320's Avatar
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    Re: What causes CH to rise?

    Water evaporates, the Calcium in it stays behind. 675 doesn't sound all that high to me - I've gone into 4 figures before!

    You have low TA, so the CSI should be okay. Keep pH at the low end and you shouldn't have any problems. The only solution I have is continuously draining and refilling. I use pool water on the lawn and then refill it with lower CH tap water. I've directed one of the downspouts into the pool, which is a source of Calcium-free water, although it does tend to introduce a lot of very fine silt at the beginning of the storm. Since you run a SWG, I don't know if watering the lawn is feasible. I have no first hand experience with saltwater and grass.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: What causes CH to rise?

    What type of Chlorine and shock are you using? Those are typically the only way CH rises.

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    JasonLion's Avatar
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    Re: What causes CH to rise?

    Quote Originally Posted by PoolsPlusMI
    What type of Chlorine and shock are you using? Those are typically the only way CH rises.
    CH in fill water is the most common cause of CH increasing, though the use of cal hypo for chlorine (which also contains CH) is also a significant cause.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Mod Squad Bama Rambler's Avatar
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    Re: What causes CH to rise?

    Quote Originally Posted by PoolsPlusMI
    What type of Chlorine and shock are you using? Those are typically the only way CH rises.
    I don't know about MI, but in a part of the rest of the country where the CH out if the tap is in the 400 to 500 range, cal-hypo (while signicant) isn't the major cause of rising CH.
    Dave J. TFP Moderator
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    phalcon51's Avatar
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    Re: What causes CH to rise?

    Quote Originally Posted by PoolsPlusMI
    What type of Chlorine and shock are you using? Those are typically the only way CH rises.
    I'm using laundry bleach from Wal-Mart (6% sodium hypochlorite) for the chlorine when it's too cold for the SWCG to work and I'm not using any shock at all.
    26,200 gal. 35' x 16' Plaster IGP (50 yrs. old), Hayward 48 sq. ft. DE filter, Hayward EcoStar VS pump, Intellichlor IC-40 SWCG, The Pool Cleaner 4X suction, Pool Skim and Pool Devil skimmers. Re-plastered Sept. 2010.

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