Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 14 of 14

Thread: FAS DPD Testing - Experience needed

  1. Back To Top    #1

    In the Industry


    Join Date
    Apr 2012
    Location
    Lynchburg, VA
    Posts
    87

    FAS DPD Testing - Experience needed

    I have been using the DPD testing powder 0870 for only a short while.
    I am thoroughly enjoying the precise numbers it will give.
    But I have recently come across a head scratcher.

    I just opened a pool not 7 days ago.
    It was a bit green but nothing I couldn't handle.... Or was it?
    I initially shocked the pool with Cal-Hypo, that did most of the green in.
    I removed the dead algae by vacuuming to waste. The FC levels dropped, as expected.
    So I hit again with Cal-Hypo. And again wasted the dead algae. The water tests
    As of this morning are as follows.
    PH 7.4
    TA 95
    CH 110
    CYA 35ish
    But then I went to the reliable DPD test for the FC, and here comes the curveball. I put in the
    two scoops of 870 then I ran the next part of the test with the drops of 871. It went
    From a very light to pink to a very dark pink on the second drop. The 871 is suppose to change the pink to clear to give you the FC ppm. But it does the opposite it goes pink then pinker then clearer.
    Of course once it goes clear I test the CC with the 003 drops and get a reading of .5 or less

    When I test again using the tests strips I get a very low FC reading.
    Versus the test using the DPD and 871 drops.
    Anybody have any idea what might be going on here?
    Why is the 871 test drops turning my sample pink when it is suppose to be turning it clear?

    And to top it all off the pool is very cloudy at this point... Clearing up ...but slowly.
    Does anyone suppose the cloudiness may have something to do with this whole testing kanundrum?

    Thanks for any help here,
    PF
    The Most Interesting Pool Man in The World
    I don't always have clients that want to maintain their pool,
    but when I do, I send them to troublefreepool.com!

  2. Back To Top    #2

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,077

    Re: FAS DPD Testing - Experience needed

    Does anyone suppose the cloudiness may have something to do with this whole testing kanundrum?
    No, I doun't think they are related.


    1. Is your clear cylinder rinsed thoroughly before you perform the test?

    2. Do you have an OTO chlorine test? (the one that takes 5 drops of a yellowish reagent?) If so, do that test and report the results.

    3. Regardless that it turns it turn pinker, it still goes clear at a point that makes sense to you, right?

    4. The strips are worthless

    5. The cloudiness may be caused from using Cal Hypo. You should be using liquid chlorine to shock.

    6. What is your current FC? (using FAS/DPD and using OTO)
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  3. Back To Top    #3
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: FAS DPD Testing - Experience needed

    The clouding is not related. It could be caused by dead algae or from using cal-hypo. What is your TA?

    The variation in pink could have been caused by not mixing throughly enough just at first.
    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

  4. Back To Top    #4

    In the Industry


    Join Date
    Apr 2012
    Location
    Lynchburg, VA
    Posts
    87

    Re: FAS DPD Testing - Experience needed

    Thanks for the quick responses, but I did forget to mention that this is a vinyl pool.

    The vile seems clear to the eye. I do give it a rinse before hand as well.
    I do not have the OTO but I do have the taylor test kit.
    The FC is as of this am is .5-1 ppm
    But here is a new twist, with my results from yesterday being all in the normal range, I started
    to put some pucks in the chlorinator(tr-Chlor) and now I have a TC reading of
    6 - (this of course using the taylor test kit)
    That is a CC of 5-5.5!

    I have found that I use the strips only for a quick snapshot of what is going on
    In the water. I only rely on them as a maintenance measuring stick in between true testing with my Taylor test kit.

    I have been doing some poking around on the liquid bleach, ie Clorox. Am I not mistaken that using
    That contributes more heavily to the TDS, by adding so much inert material?

    Jason, The TA is 95

    Thanks for all your input.
    The Most Interesting Pool Man in The World
    I don't always have clients that want to maintain their pool,
    but when I do, I send them to troublefreepool.com!

  5. Back To Top    #5

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,077

    Re: FAS DPD Testing - Experience needed

    Am I not mistaken that using That contributes more heavily to the TDS, by adding so much inert material?
    It adds salt (which is calculated in TDS) but TDS is irrelevant in the first place.

    You either have some testing issues or you really need to shock the pool. CC's of 5 or so would indicate a DESPERATE need to shock. Has your pool water ever been clear since you added the Cal Hypo?

    .5 - 1ppm FC is not nearly enough FC.

    Please read the article up in Pool School on "How to Shock your Pool" . It is beginning to sound like you have never completed the process.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  6. Back To Top    #6

    In the Industry


    Join Date
    Apr 2012
    Location
    Lynchburg, VA
    Posts
    87

    Re: FAS DPD Testing - Experience needed

    Thank you David.

    I promise you I have shocked quite a few pools quite a few times, with great success
    Using Cal Hypo

    I think maybe I have given far too much info about my pool situation, and lost focus on
    What question I am trying to get help on.
    I do make mistakes when it comes to pool care, that is for sure. And this most likely falls into
    That category.
    But please if you can help with the DPD question that is where my main concern is.
    I have never seen this particular test act this way and I was hoping to have some light shed on it.
    My guess at this point is because the CC was so high, and I am sure I got it there while trying kill the algae, ...that may be what is affecting the testing in this way.

    Do you think that the DPD powder or the 871 drops can go bad?

    Thanks again.

    And thanks for the freshing up on the "how to shock your pool" it was a good read.
    The Most Interesting Pool Man in The World
    I don't always have clients that want to maintain their pool,
    but when I do, I send them to troublefreepool.com!

  7. Back To Top    #7

    Re: FAS DPD Testing - Experience needed

    If the FC is high, the indicator may have been partially bleached out. The titrating reagent (R-0871) reduces the FC and the indicator is no longer being bleached out.

    If the indicator completely, or partially, bleaches out, add an extra scoop of R-0870 powder and do the test as normal.

    Alternatively, you could dilute the test sample water with 50 % distilled water and the multiply the result by 2.

    Have you used a "Yellow-out" type product in this pool?

    Also, since you routinely shock pools, get some OTO to use as a verifier. OTO won't bleach out and can help identify the existence of high chlorine levels.

  8. Back To Top    #8

    In the Industry


    Join Date
    Apr 2012
    Location
    Lynchburg, VA
    Posts
    87

    Re: FAS DPD Testing - Experience needed

    To all thanks for your help with the DPD mystery.

    But I think it may be solved.

    I believe the high CC was messing with the the Powder and the 871 drops.
    After a thorough shocking last night, I tested again this morning and the DPD powder and
    871 drops worked perfectly. An FC reading of 2, Then I tested the CC with the 003 drops and I am happy to report A big fat zero for CC.
    All of these numbers were confirmed with the drops from the other Taylor test kit.
    So, for all those that may run into this DPD issue in the future, check those CC numbers.
    .... Of course try not to get yourself into this mess in the first place.

    Thanks again to all.
    Looking forward to further discussion.

    PF
    The Most Interesting Pool Man in The World
    I don't always have clients that want to maintain their pool,
    but when I do, I send them to troublefreepool.com!

  9. Back To Top    #9
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: FAS DPD Testing - Experience needed

    When the CC level is much higher than the FC level, CC can "leak" through into the FC portion of the test if you don't move the test along quite quickly. That could result in exactly what you describe, the pink getting more intense as CC contaminated the FC portion of the test.
    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

  10. Back To Top    #10

    Re: FAS DPD Testing - Experience needed

    Quote Originally Posted by Pool_Fool
    After a thorough shocking last night, I tested again this morning and the DPD powder and
    871 drops worked perfectly. An FC reading of 2, Then I tested the CC with the 003 drops and I am happy to report A big fat zero for CC.
    You shocked it last night, and the FC this morning is only 2 ppm?

    How much chlorine did you add to how many gallons?

  11. Back To Top    #11

    In the Industry


    Join Date
    Apr 2012
    Location
    Lynchburg, VA
    Posts
    87

    Re: FAS DPD Testing - Experience needed

    There was a CC level of 4.5 that had to be burned out.
    Once that was Burned out all that was left was the FC and that was only 2.
    The pool is about 25,000 gallons. I added 17lbs of Cal-hypo.
    Isn't chemistry fun!?!
    The Most Interesting Pool Man in The World
    I don't always have clients that want to maintain their pool,
    but when I do, I send them to troublefreepool.com!

  12. Back To Top    #12

    Re: FAS DPD Testing - Experience needed

    17 pounds of 65 % calcium hypochlorite will provide 53 ppm of chlorine to a 25,000 gallon pool. The 4.5 ppm of CC would only require 2.25 additional ppm of chlorine to oxidize the CC. Therefore, there has to be something else going on.

  13. Back To Top    #13

    In the Industry


    Join Date
    Apr 2012
    Location
    Lynchburg, VA
    Posts
    87

    Re: FAS DPD Testing - Experience needed

    That was the number I was shooting for. I was increasing the FC to ten times the CC(with a little extra, to be safe and get it) to release the chlorine lock.

    That is how I have learned to remedy that issue. It has worked for years, and if it ain't broke
    Don't fix it!.

    Do you know some other method?

    Thanks
    PF
    The Most Interesting Pool Man in The World
    I don't always have clients that want to maintain their pool,
    but when I do, I send them to troublefreepool.com!

  14. Back To Top    #14

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,077

    Re: FAS DPD Testing - Experience needed

    Chlorine lock is a myth.

    Do you know some other method?
    not so much a method but a better understanding can be found in Pool School above
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •