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Thread: Which test is more reliable?

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    Which test is more reliable?

    I am using the TF test kit with two different chlorine test options. There is the simple test and the one that uses the 870 powder to test above 5PPM or more accurately (according to the instructions). I ran my Aqua Rite overnight on super chlorinate because we had gotten some rain and when I tested this morning it was pretty week yellow on the quick test. Maybe between one 1 and 2 ppm. So I tried using the other test to be more accurate. it gave me a reading of 7PPM. which one of these should I trust?
    thanks for the help.

    Tim Schandorff
    I have a 25K IG pool (concrete)
    I live in the Caribbean with poor infrastructure and lose power often.
    Hayward pump, Hayward clear star plus cartridge filter
    New to pool ownership

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    BoDarville's Avatar
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    Re: Which test is more reliable?

    I would go with the test that uses the powder (a.k.a., the FAS-DPD test).
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    Re: Which test is more reliable?

    I would say trust the powder test. The color test can be very subjective depending on the background of the clear tube. Was the water for both from the same sample? I began using a turkey baster so that I can get a sample from 2' down and fill a cup that I then use for all tests. And avoid getting the sample from near a return. Do you have the speedstir? If not, make sure you constantly shake the vial while adding drops. Hope this helps!
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    Richard320's Avatar
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    Re: Which test is more reliable?

    Quote Originally Posted by tim_schandorff
    I am using the TF test kit with two different chlorine test options. There is the simple test and the one that uses the 870 powder to test above 5PPM or more accurately (according to the instructions). I ran my Aqua Rite overnight on super chlorinate because we had gotten some rain and when I tested this morning it was pretty week yellow on the quick test. Maybe between one 1 and 2 ppm. So I tried using the other test to be more accurate. it gave me a reading of 7PPM. which one of these should I trust?
    thanks for the help.

    Tim Schandorff
    If you used the 25 ml sample, your FC would be more like 2.8, which tallies better with the OTO test. It's a common mistake.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    JasonLion's Avatar
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    Re: Which test is more reliable?

    The FAS-DPD test is better in nearly every way, but it is more work and more expensive. The OTO test is terrible for trying to figure out a precise FC level. The greatest strength of the OTO test (drops turn the sample various shades of yellow) is for checking for chlorine vs. no chlorine, which the FAS-DPD test occasionally gets wrong.

    Many people use the OTO test for quick daily testing just to make sure they haven't somehow lost all of their chlorine, and then use the FAS-DPD weekly to figure out the exact amount of chlorine to add each day. Others prefer to use the FAS-DPD test all of the time.
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    UN1017's Avatar
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    Re: Which test is more reliable?

    I second that. The DPD-FAS is more cut and dry compared to the OTO test. Since you are looking for color change instead of shade of yellow it seems more accurate. However, the math component (x .5) can be an error factor.

    7 ppm should have clearly been yellow (5 ppm +) on the OTO. I would double check your test process for errors (math, sample sizes etc.)
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    Re: Which test is more reliable?

    Quote Originally Posted by Richard320
    If you used the 25 ml sample, your FC would be more like 2.8, which tallies better with the OTO test. It's a common mistake.

    The test instructions said to use 10ml for the sample size so that's what I used? Is there a reason to use 25ml?

    Thanks everyone for the feedback.

    Tim
    I have a 25K IG pool (concrete)
    I live in the Caribbean with poor infrastructure and lose power often.
    Hayward pump, Hayward clear star plus cartridge filter
    New to pool ownership

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    Re: Which test is more reliable?

    Do you have any cc? Did you do either test near a return?

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    Re: Which test is more reliable?

    Not trying to hijack the thread.. but with the Taylor k-2006 which FC test is more accurate the 10ml with 2 dippers or the 25 ml. with the 2 dippers?
    21,500 Gallon Vinyl liner pool Eastern Pennsylvania
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    Re: Which test is more reliable?

    25 ml is more accurate (per the instructions) but for our purposes, that much accuracy is a bit pointless.
    Dave S.
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    Re: Which test is more reliable?

    Quote Originally Posted by duraleigh
    25 ml is more accurate (per the instructions) but for our purposes, that much accuracy is a bit pointless.
    Thanks the 25ml is the test I have been using for the OCLT test.
    21,500 Gallon Vinyl liner pool Eastern Pennsylvania
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    Re: Which test is more reliable?

    One more thing make sure you hold your dropper bottle inverted as shown in this video http://www.youtube.com/watch?v=PHQG4tgQsFE studies have shown that drop size can vary considerably when held at any other angle.

    Ike
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