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Thread: Calcium Hypochlorite w/ Plaster Pool

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    Calcium Hypochlorite w/ Plaster Pool


    The pool store we used to go to went out of business last year, so I decided to go to Leslie's this year. They recommended calcium hypochlorite instead of the sodium based chlorine that I used previously. After purchasing the calcium hypochlorite, I noticed in my notes from when we first had the pool installed "Never use calcium based chlorine!". Can anyone explain the dangers of using calcium based chlorine with a plaster pool? Thank you.
    27 ft round AG, vinyl, 17,100 gallons, 2 HP pump, sand filter

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

    Re: Calcium Hypochlorite w/ Plaster Pool

    Welcome to TFP!

    It is important to keep you calcium level in an appropriate range. Cal-hypo adds calcium to the water. If you are constantly adding calcium, your calcium level will eventually get too high and you will get calcium scaling. Calcium scaling makes the pool surface rough, causes white marks on colored finishes, and is quite difficult to remove.

    If your calcium level is current very low, it might be fine to use cal-hypo for a while. But long term it is very likely to cause problems.
    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
    Jun 2007
    New Jersey

    Re: Calcium Hypochlorite w/ Plaster Pool

    The manual that Anthony-Sylvan gave me back in 2004 made the same prohibition without explanation. [I only just noticed it.] I have a white plaster pool and I use Cal-Hypo whenever I need to raise CH level (mainly in the Spring to replace fall draining). I control my CH and have had no problems. They were making plaster pools long before CYA came into use; I wonder what they told people back then.

    I believe they assume that controlling CH is too hard for their new pool owners so they just tell them to avoid Cal-Hypo to make their own lives easier (by avoiding scaling complaints). With a colored plaster pool, I would be more cautious, however.
    Current: 28,000G 18'x36' I/G AnthonySylvan Plaster; Waterway 60 sq.ft. DE Filter; 1.0hp x 1.65 SF Two-Speed (B2982) WhisperFlo; 2004-Present
    Previous: 40,000G 20'x40' I/G Koven unlined WWII salvage 5/8" marine steel; Lomart Stainless Sand Filter; 3/4hp Hayward SuperPump; 1946-2003 (managed by me from about 1964)
    Ancient Taylor K-2000, upgraded with Taylor CH, TA, and FAS-DPD, and TFT CYA tests.

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