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Thread: Understanding chemical readings

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    Understanding chemical readings

    hi

    This is the first year I try to maintain the pool chemicals. This is probably a stupid question, but here it goes

    I recently got my TF-100 test kit. I am trying to understand the difference (if any) between CL and FC. When I measure Cl with the K-1000 set, I usually read between 2 and 3. However when I do the FC test, I get 4 ppm. CC is 0. So should FC and Cl be the same?

    Also, is there a way to test exactly the PH. Based on the K-1000 set again, the Ph is usually between 7.2 and 7.5. i am just curious to know if I can find the exact reading somehow with the TF-100 kit.

    The rest of the results are
    TA 110
    CH 230
    CYA 20

    Regarding the CYA reading, should the black spot disappear completely or is the reading to be taken when the black spot becomes grey?

    We have a 22000 gallons pool, with a DE filter, and we just had it replastered.

    Thanks. Callyann
    24' x 54" AG Sharkline Matrix.
    Pentair PNCC0150OF2160 Clean & Clear 150 Sq' Cartridge Filter System with 1-1/2HP Dual Speed OptiFlo Above Ground Pool Pump
    Installing May 2013.
    Deck to be installed soon after..I hope.

  2. Back To Top    #2
    Mod Squad jblizzle's Avatar
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    Re: Understanding chemical readings

    There are extended test instructions in a sticky in the Testing Forum that should answer all your questions.

    The OTO chlorine test measures total chlorine ... it is not really surprising that they do not match ... trust the FAS-DPD test.

    That is the only pH test. Nothing more exact is available.

    Dot should be totally gone and lighting during the test is very important.

    Posted from my Droid with Tapatalk ... sorry if my response is short
    Jason, TFP Moderator
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    Re: Understanding chemical readings

    Thanks Jason for your prompt answer.

    From your answer I understand that FC is the FAS/DPD test and CL is the OTO test. However, you said OTO measures total chlorine but it reads as between 2 and 3 and as I said, CC with the FAS/DPD test is 0 yet FC is 4 ppm so it is still not making sense to me BUT as you suggest, I will trust the FAS/DPD.

    Not sure what you mean by "......In a sticky in the testing forum". I don't know what a sticky is in that context.

    Thanks for claryfing the disappearance of the black dot. Next time I will make sure I am in full light.
    24' x 54" AG Sharkline Matrix.
    Pentair PNCC0150OF2160 Clean & Clear 150 Sq' Cartridge Filter System with 1-1/2HP Dual Speed OptiFlo Above Ground Pool Pump
    Installing May 2013.
    Deck to be installed soon after..I hope.

  4. Back To Top    #4

    Re: Understanding chemical readings

    Here is a link to the "sticky" referred to. Sticky is like an electronic post-it note and they are at the top of each index category.

    extended-test-kit-directions-t25081.html
    POOL: Intex ultra new in 2014 (32 x 16 x 52) (seasonal; on concrete pad covered with 1.5" extruded or whatever foam insulation sheets - ugly, but comfy); added a through-wall skimmer; I add salt for feel. EQUIPMENT: Pentair SuperFlo pump (1HP, 2SPD); Pentair cartridge filter (200 sq. ft); Pentair MasterTemp natural gas heater (400,000 btu) Climate/Location: Eastern Nebraska

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    UnderWaterVanya's Avatar
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    Re: Understanding chemical readings

    OTO is very subjective. Easy to have minor errors. FAS-DPD is more accurate.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

  6. Back To Top    #6

    Re: Understanding chemical readings

    Thanks everyone for your answers and link, very helpful
    24' x 54" AG Sharkline Matrix.
    Pentair PNCC0150OF2160 Clean & Clear 150 Sq' Cartridge Filter System with 1-1/2HP Dual Speed OptiFlo Above Ground Pool Pump
    Installing May 2013.
    Deck to be installed soon after..I hope.

  7. Back To Top    #7

    Join Date
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    SE Minnesota
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    91

    Re: Understanding chemical readings

    Quote Originally Posted by nonasdada
    Thanks Jason for your prompt answer.

    From your answer I understand that FC is the FAS/DPD test and CL is the OTO test. However, you said OTO measures total chlorine but it reads as between 2 and 3 and as I said, CC with the FAS/DPD test is 0 yet FC is 4 ppm so it is still not making sense to me BUT as you suggest, I will trust the FAS/DPD.
    CC = combined chlorine and you want this to be .5 or less
    FC = free chlorine
    TC = total chlorine = FC + CC
    Mona SE MN
    24' round 48" high AG
    Meteor Sand Filter
    1.5 HP pump

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