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Thread: Odd results with FAS-DPD test

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    Odd results with FAS-DPD test

    Recently when testing a pool using a K-2006, the water sample would barely change colour when the DPD powder was added. But when the titration agent was added, the colour would get darker and darker with every drop until after about 5 drops, at which point it would lighten again as is normal. On a 10mL sample test, total drops was 10 before it went clear again.

    In subsequent re-tests, I tried 10mL and 25mL samples, and I tried adding several extra dippers of DPD powder (to make sure there was enough in case of high chlorine), all with similar results. A test strip showed somewhere around 8-10ppm, but not dark enough that it looked >10.

    What was happening?
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Odd results with FAS-DPD test

    That's a mystery. You might try calling Taylor Technologies on that one. Be sure to thoroughly stir after adding the powder since it normally keeps getting darker as it mixes. I've seen it do a flash of pink at high FC, but adding more powder shows up as red. You did everything right.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Odd results with FAS-DPD test

    It was thoroughly mixed - after a couple of frustrating tries I even added the cap and shook the **** out of it just to be sure! In matter of fact, during the part where adding drops made the water pinker, the water would start to lighten back up if left for a few seconds.

    If it happens again I will try to call Taylor direct.
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Odd results with FAS-DPD test

    How old are the reagents?
    20k gallon IGP
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    TF100 test kit w/ speedstir

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    Re: Odd results with FAS-DPD test

    Kits are about ten weeks old. R-0870 and R-0871 were refilled about two weeks ago from 470mL bottles purchased three weeks ago.
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Odd results with FAS-DPD test

    What are the lot numbers on the 473 mL bottles?

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    Re: Odd results with FAS-DPD test

    I spoke directly with Taylor Technologies today. They say that what I am seeing can be normal with an excessively high chlorine level; simply make sure there is enough DPD powder in the tube (add more until there is some crystallized and left over at the bottom) and keep adding reagent until the colour clears up again, and stays clear for 20-30 seconds.

    I had a similar effect today, but today the test was only 6.5ppm FC - hardly an excessive chlorine reading. So I'm still confused, but taking Taylor's word that the test is still accurate.
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Odd results with FAS-DPD test

    For whath it is worth, I just did the same test tonight with a result of FC of 6.5 with CYA of 45 and had the "normal" results - not what you are having. I have never seen that even when my FC was 40 with a CYA of over 200.
    Viking Pools Freeport 12' x 25' Fiberglass 6000 Gallon Screened - Hayward Pro-Grid Vertical D.E. Filter DE2420 Hayward Superpump 1HP - Zodiac Pacer Cleaner - Pool Pilot Digital - TF-100 test kit - Central Florida Thanks to TFP Pool School, SWCG and the Pool Calculator, taking care of the pool is easy!

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    Re: Odd results with FAS-DPD test

    Hilton,

    I hope you eventually solve this puzzle. The trouble is that you are caring for pools that are not your own. Heaven knows what in the world the client is putting in their pool water unbeknownst to you---fun water colors not to mention the myriad things people toss into a pool during a party.

    How does this water look to you? How often are you called upon to service this pool?

    How many different sets of reagents do you have?

    Just wondering.....I love a good mystery....

    Lana
    23,600 gallon, refurbished 1960's inground concrete, Jandy sand filter w Jandy 2 hp variable speed pump, Pool Pilot Digital SWCG+Chemtrol 2100+CO2 tank; PebbleTec White Pearl with 10% Cobalt Blue Dark Beadcrete by Olympic Pool Plastering, Georgia. Taylor K-2006 Test Kit; Aqua Check Salt test; LaMotte borates test, and Jack's Magic Sequest test kit; SparklyPoolitis level: extremely high.

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    Re: Odd results with FAS-DPD test

    I routinely test much higher with normal response as well. I maintain these pools once per day Mon-Fri, with a volunteer doing evening and weekend testing (per my other recent thread).
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    JasonLion's Avatar
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    Re: Odd results with FAS-DPD test

    The FAS-DPD test can bleach out if you don't use enough powder. What you describe sounds like there was not enough powder, and the test was just starting to bleach out but hadn't bleached out completely. Adding drops progressively lowers the FC level, which first went to eliminating the partial bleaching out, and subsequently worked normally.

    That only fits what you described if you accidentally used quite a bit too little powder. Between the tiny spoon and the occasional fairly large grains in the R-0870 that can happen sometimes, though it doesn't really seem likely. This kind of problem is much more common when the FC level is really high, say 25+, where extra powder is always required. Still, it seems like something along these lines must have been happening.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Odd results with FAS-DPD test

    Quote Originally Posted by Hilton
    Kits are about ten weeks old. R-0870 and R-0871 were refilled about two weeks ago from 470mL bottles purchased three weeks ago.
    I don't think that R-0870 comes in a 470 ml size. R-0870 comes measured by mass (grams) or weight (pounds), not volume.

    R-0871-E does come in a 16 ounce bottle, which is 473 ml.

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    Re: Odd results with FAS-DPD test

    Sorry, the R-0870 was refilled from a fresh 1/4lb bottle. *I* know what I meant!
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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