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Thread: CH decreasing on new plaster

  1. Back To Top    #1

    Join Date
    Aug 2008
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    Maryland
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    CH decreasing on new plaster

    I'm puzzled by the steadily declining behavior of CH that I'm seeing as I startup our new pool. I'm testing with the the TF-100 kit, aiming for a neutral startup of new white plaster in 50K gal pool. It was plastered/filled Friday.

    The fill water tested at pH 7.8, TA 100, and CH 200, with fill completed at 7:30pm. I added the sequestering agent that the plasterers provided, during the last of the fill. Builder's startup operation advised I do nothing else until our appt. the next morning.

    At 7:30am Saturday, numbers were pH 8.2, TA 125, CH 185. The builders startup crew arrived at 9 am Saturday, installed the floor cleaning heads and other bits, and started the pumps. Over the course of the day, I added 3 gallons of muriatic acid, and brushed 3 times, resulting in 10pm numbers of pH 7.0 TA 70 CH 180. 8am Sunday, pH 7.2 TA 85 CH 170. 3 rounds of brushing, pH rising over the day, eventually at pH 7.8 TA 80 CH 140. Added 1 gallon acid, bringing pH down to 7.2.

    I thought that the curing plaster would be contributing some dissolved calcium compounds to the pool water, so am puzzled that CH could go 200->185->180->140 as we brushed, filtered, and added acid.
    Chem gurus?
    52k gal/1300sqft white plaster wi spa, 2 Intelliflo 4x160, 2 C&C 420, Heat Siphon heat pump, PCC-2000, Intellitouch, CL&MA injection

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: CH decreasing on new plaster

    That is probably the sequestrant binding up the excess calcium. CH will start going up soon.
    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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    Join Date
    Aug 2008
    Location
    Maryland
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    Re: CH decreasing on new plaster

    Thanks Jason, sounds reasonable. I will go easy on the CaCl addition I was planning for this evening, perhaps only aim to bring it up to 160-170.
    By the way, thanks for the pool calculator!
    52k gal/1300sqft white plaster wi spa, 2 Intelliflo 4x160, 2 C&C 420, Heat Siphon heat pump, PCC-2000, Intellitouch, CL&MA injection

  4. Back To Top    #4
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: CH decreasing on new plaster

    You shouldn't add any calcium to a pool with fresh plaster for about the first 30 days unless the plaster people tell you to. As the plaster cures it will raise the PH, TA, and CH levels. This happens rapidly for the first three or four weeks, and then more slowly for up to a month. If you add CH early on, and it then goes up significantly, you can easily end up at a very high CH level that you don't want.
    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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