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Thread: Comparison of three methods to half the CYA

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    Comparison of three methods to half the CYA

    1) drain 1/2 the water (in one shot) and refill. Cost: 50% of the pool water capacity
    2) drain 1/4, refill (now CYA is 3/4), drain (1/4) refill (now CYA is 0.56), drain (12%) and refill. Cost: 62% of pool water capacity
    3) drain 5% refill (now CYA is 95%), drain 5% refill (now CYA is 90%), etc ...
    you need to drain and refill log0.95(0.5)=13.51 times. Water cost 67.5% of the pool water capacity

    So if you can drain only once exactly as much as you need.

    For me, 17% of pool capacity is about $30

    Note: if you need to divide CYA by four and drain only 5% at at time, water cost is 1.35 times the pool water capacity - almost double the cost compared to draining once.
    19'500 gallons in-ground pool and SPA, painted white over black plaster, 1hp Sta-Rite with A.O. Smith B2982 2-speed motor, 136 sqft cartridge filter, currently overhauling a 400'000 BTU Teledyne Lars Mark V heater. Converted to 12v LED party lights. 20-mule team borax saved me from algae depression. San Diego CA

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

    Re: Comparison of three methods to half the CYA

    In some situations draining 5% at a time is the only practical choice. In those cases, paying for an extra 17.5% of water is not really that big a deal.
    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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