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Thread: Inconsistent CYA test results

  1. Back To Top    #1

    Join Date
    Sep 2010
    Location
    Tampa, FL
    Posts
    14

    Inconsistent CYA test results

    As the title of this thread implies, I've been getting inconsistent CYA test results. I have a test kit with the black dot CYA test. Sometimes I get 30ppm, sometimes closer to 60ppm.

    I've been maintaining chlorine levels consistent with CYA=60ppm just to be safe (actually a little higher due to above average sunlight, heat and bather load).

    So for CYA=60, minimum FC is 5 and target FC is 7.

    If CYA=30, minimum FC is 2 and target FC is 4.

    Daily FC demand has been 3.5-4.0ppm, and I've found that raising FC to 10ppm at night allows me to remain safely above the minimum FC=5ppm for CYA=60ppm.

    The question is, what if my CYA is actually 30ppm? Is FC=10ppm too high to swim in? I vaguely remember someone saying that it's ok to swim as long as FC is under shock levels, which for CYA=30ppm is 12ppm.

    BTW, the pool store test result for my CYA is always minimum 100ppm (as high as they will test).

    Thanks!

    Doji
    15,000 gallon outdoor in-ground plaster pool
    Sand filter flow rate 62 GPM
    3/4hp pump

  2. Back To Top    #2
    linen's Avatar
    Join Date
    Jul 2010
    Location
    Twin Cities, MN
    Posts
    8,649

    Re: Inconsistent CYA test results

    Have you looked at the extended directions for the TF100 CYA test? http://www.troublefreepool.com/exten...1.html#p206397 Might be something in there that helps you. I would disregard the store testing, if you want to check you technique, order the 50 ppm reference solution from tftestkits.net.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  3. Back To Top    #3
    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    Location
    SouthWest Alabama
    Posts
    22,347

    Re: Inconsistent CYA test results

    Standing with your back to the sun is the best way to do the black dot test. Your result will be more accurate that way.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

  4. Back To Top    #4

    Re: Inconsistent CYA test results

    Quote Originally Posted by linen
    Have you looked at the extended directions for the TF100 CYA test? http://www.troublefreepool.com/exten...1.html#p206397 Might be something in there that helps you. I would disregard the store testing, if you want to check you technique, order the 50 ppm reference solution from tftestkits.net.
    I got the 50 ppm solution for reference.

    When I tested it I would have read it as ~70ppm if I didn't know it was 50ppm.

    Evidently the black dot has to totally disappear.

    As result my pool which I had previously thought was around 40 ppm was probably really below 20 ppm. I have added some CYA using triclor and think I am back above 30 ppm.

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