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Thread: Maybe I'm not understanding my OTO test

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    Maybe I'm not understanding my OTO test

    Quote Originally Posted by Richard320 View Post
    The OTO test that comes with the TF100 gets darker and darker as FC levels increase.
    Last week, my FC was 10 as tested with the FAD-DPD test in my TF-100, but the OTO test looked like it was around 5. Any idea why that would be? I'm thinking of getting a K-2000 to replace the K-1000 as my CYA level of 80 for my SWG pool has a target FC of 6, but maybe I'm not understanding my OTO test.

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    JasonLion's Avatar
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    Re: Maybe I'm not understanding my OTO test

    Most people can't distinguish between the various similar yellows from the OTO test when FC is anywhere between 3 and 11 or 12. The OTO test is very reliable at distinguishing between chlorine and no chlorine, but it isn't very good for determining what the specific FC level actually is.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Mod Squad zea3's Avatar
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    Re: Maybe I'm not understanding my OTO test

    The OTO test is not precise and gives at best a ballpark estimate of FC for 5ppm and under. Having to match color to read the result makes the test more subjective, and it is not designed to measure FC >5ppm, even though it does turn darker with higher FC. Your FAS-DPD test will give a more precise result and is the test you should use when determining levels to balance the pool.
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    Re: Maybe I'm not understanding my OTO test

    Quote Originally Posted by zea3 View Post
    Your FAS-DPD test will give a more precise result and is the test you should use when determining levels to balance the pool.
    I understand that the FAS-DPD test is the most accurate way to determine my FC and CC. However, for daily testing, I'd rather not use the FAS-DPD as it takes longer to perform and would quickly use up all of the reagents.

    For daily testing, does anyone use and would recommend the 1-10 ppm chlorine test in the Taylor K-2000?

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    Mod Squad jblizzle's Avatar
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    Re: Maybe I'm not understanding my OTO test

    Keep the OTO at a deep yellow then use the FAS-DPD at least once a week ... order more reagent when you need it. It is not that expensive.
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    JasonLion's Avatar
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    Re: Maybe I'm not understanding my OTO test

    There are different ways to do things. I use the FAS-DPD test once a week to calculate how to adjust my chlorine dosage, and then use OTO daily just to make sure things haven't gotten completely out of hand. Others prefer to use FAS-DPD daily.

    To my view, the DPD test is a compromise all around. It is better than the OTO test for measuring levels, but not as good as FAS-DPD. Also, it will read FC at zero when FC is above 10, which can cause problems. I would rather go for something dead simple (OTO) or very precise (FAS-DPD) depending on my needs at the moment, instead of compromising.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Maybe I'm not understanding my OTO test

    Maybe it's because I just got my pool a few months ago and this is my first fall, but the chlorine levels are all over the place with the crazy Texas weather we have. I guess I'm just looking for a quicker way to at least make sure my chlorine level is between 5 and 10 to know if I should dial the SWG up or down a few percent. If I'm testing daily, then the DPD test bleaching out when the FC is above 10 wouldn't really be a problem since a true reading if 0 would mean that the FC dropped more than 6 in one day, which seems pretty unlikely. I'll probably go ahead and order a K-2000 and give it a try. Worst case, I have another thing collecting dust on the shelf and I get some more phenol red.
    23K gal, 38' x 22' irregular, gunite, StoneScapes Mini Pebbles, 2 HP TriStar 2spd pump, 525 sqft cartridge filter, TurboCell SWG, ProLogic controller, The Pool Cleaner 2 Wheel

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