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Thread: Regular DPD test for maintenance - unreliable?

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    Join Date
    Jun 2014
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    Regular DPD test for maintenance - unreliable?

    Hi all,

    As the weather warms up, I'm determined NOT to start the season with a green pool as was the norm. I didn't get too lax over the winter and so the sudden increase in chlorine usage is not going to catch me by surprise thanks to everyone here.

    My question today is if reagents can go bad? I grabbed my DPD test and got a zero reading for FC. It freaked me out so I pulled out my K2006 (FAS-DPD) and found a reading of 3ppm (pH matched between the two tests). The 'basic' kit is at least a year, if not two, old.

    If so, I have to decide if I want to just use my full test a few times a week or replace this kit so I only use the K2006 on the weekends (like I did the second half of last summer once things were in stasis). Your opinions on this would be nice too.
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Divin Dave's Avatar
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    Oct 2013
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    Re: Regular DPD test for maintenance - unreliable?

    There are some of the regents that can go bad after a couple of years.
    tftestkits actually has a sale going on this month for regent replacements.

    Quote Originally Posted by Gig103 View Post
    Hi all,

    As the weather warms up, I'm determined NOT to start the season with a green pool as was the norm. I didn't get too lax over the winter and so the sudden increase in chlorine usage is not going to catch me by surprise thanks to everyone here.

    My question today is if reagents can go bad? I grabbed my DPD test and got a zero reading for FC. It freaked me out so I pulled out my K2006 (FAS-DPD) and found a reading of 3ppm (pH matched between the two tests). The 'basic' kit is at least a year, if not two, old.

    If so, I have to decide if I want to just use my full test a few times a week or replace this kit so I only use the K2006 on the weekends (like I did the second half of last summer once things were in stasis). Your opinions on this would be nice too.
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge.
    www.tftestkits.net Experience- it's what's learned just after you needed it most !!

  3. Back To Top    #3
    BoDarville's Avatar
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    Re: Regular DPD test for maintenance - unreliable?

    If your basic kit is more than two years old, I would not use those reagents. Plus, depending on where you purchased the basic kit, there's no telling how long it may have been sitting on the store shelf. Given your experiment, I would trust the results of the K2006.

    As is the case with the TF-100 kit (what I use), you can purchase the chlorine reagent refills for the K-2006 (the R-0870 powder along with the R-0871 & R-0003 liquid reagents) This is what I do. These reagents will give you everything you need to test chlorine levels (FC, CC, and TC). In fact, there is an XL Option which bundles the R-0870 powder and R-0871 at a cost savings vs. purchasing separately.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

  4. Back To Top    #4

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    Re: Regular DPD test for maintenance - unreliable?

    So the consensus is to always use the 0870-0871 instead of new DPD? I ask because the tf100 also comes with an oto kit.
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    JasonLion's Avatar
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    Re: Regular DPD test for maintenance - unreliable?

    Each of the tests has pros and cons. The OTO test is very quick and simple to use, but essentially only gives you a chorine/no chlorine indication. FAS-DPD is the only one that measures above and FC of 10 and has the best precision, but is also the most work and the most expensive. The DPD test has a limited range and suffers from false negatives (can read zero when the FC level is high). If it had a wider range it might be worth it, but as is it hasn't proven very useful.

    If you are SLAMing the pool, you really need the FAS-DPD test.

    Many people around here use the OTO kit six days a week just to make sure nothing has gone really wrong, and then use FAS-DPD once a week to get an exact level and figure out dosing. Others prefer to use FAS-DPD all the time.
    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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    Divin Dave's Avatar
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    Re: Regular DPD test for maintenance - unreliable?

    If I wanna absolutely know what my FC is, I use the FAS/DPD. If I want to test for CC, then I can only do this iwth the FAS/DPD
    I use the OTO often for the sake of a quick check now and then. Especially in winter time.

    Also, many of us and others may well be keeping our FC above 5, because we have SWG's where we recommend higher FC/CYA levels than the OTO can handle. The OTO can only measure up to 5, not above, and the accuracy of it is subjective because of the necessity to compare colors.

    OTO also cannot measure CC independently of FC, so the OTO is basically measuring Total Chlorine which in itself isn't exactly indicative of how much FC you have.


    Quote Originally Posted by Gig103 View Post
    So the consensus is to always use the 0870-0871 instead of new DPD? I ask because the tf100 also comes with an oto kit.
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge.
    www.tftestkits.net Experience- it's what's learned just after you needed it most !!

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