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Thread: Dichlor and Cyanuric Acid

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    Dichlor and Cyanuric Acid

    I have read that Dichor ( dichloro-s-triazinetrione dihydrate) is about 57% cyanuric acid. I have only 3700 gallons of water and started using dichlor yesterday. Last night , using the calculator, I took my pool to 3ppm FC. The PH was 7.5. Water is beautiful. I used 2.5 oz by volume to get it to the 3ppm. My CYA was 0. I tested this morning and the FC was 2ppm, PH 7.6. This evening I tested again. FC .5 PH 7.5. I added 3 oz Dichlor by volume to take it to 4 ppm. I waited a few hours and decided to test CYA for the first time. I also tested FC 5 ppm PH 7.6 CYA 0!! I don't understand why I have not built up any CYA. I am using an HTH 6 way tester. The water I put into the clear tube with the black dot on the bottom was crystal clear. I know my test kit is junk. I know I need the whiz bang TF tester but it cant be 100% wrong. How much Dichlor would I have to feed a 3700 gallon pool to get a CYA of 40?

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    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Dichlor and Cyanuric Acid

    It can take several days for CYA to register on the test.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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

    Re: Dichlor and Cyanuric Acid

    The CYA test won't read CYA levels below 20 (or 30) at all. It also isn't precise enough to distinguish a couple of ppm of CYA added or removed.

    Dichlor adds 0.9 ppm of CYA for every 1.0 ppm of chlorine.

    You can use the Pool Calculator to figure out quantities.
    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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    frustratedpoolmom's Avatar
    Join Date
    May 2007
    SWSuburban Chicago, IL

    Re: Dichlor and Cyanuric Acid

    It will take you between 11-14 days using the same amount of dichlor each day to reach a CYA of around 40.
    The "Effects of Adding Chemicals" section of the Pool Calculator tells you how to calculate this.
    2 days of dichlor isn't even enough to reach a CYA of 10... the test vial only goes to 30 so you won't show up as having any for quite a while.

    Please keep all your pool testing related questions on one thread rather than start a new one. Thanks
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
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