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Thread: Can old DPD powder show inaccurate high reading ?

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    Can old DPD powder show inaccurate high reading ?

    When opening my pool today I put two gallons of 10% chlorine in the spillover spa to help clean it up before firing up the pump. Before running the pump I tested the water in the pool and was very surprised how high the chlorine level was. Could my DPD powder from last year give a false reading ?


    CC 4.5
    PH 4.7
    TA 140
    CH 310
    CYA 65
    Salt 2.9 per Aqaupure
    Water temp 50%



    Now I have the pump running so the spillover spa with the two gallons of chlorine is mixing with the pool water.
    I already ordered new DPD powder but it probably won't get here for a few days.
    20*40 Liner 2'-8' deep, Spill Over SPA, Electric Cover, Jandy Purelink (Aquapure & PDA), Hayward SP2610x15 (1.5HP Single Speed), Hayward H300 (Millavolt)

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    Mod Squad Bama Rambler's Avatar
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    Re: Can old DPD powder show inaccurate high reading ?

    I'd test it again since the pump is running and see what it reads.
    It's possible for the FC you read to be correct.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    JasonLion's Avatar
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    Re: Can old DPD powder show inaccurate high reading ?

    DPD powder can go bad, but it takes a really long time if you store it properly.
    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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    Re: Can old DPD powder show inaccurate high reading ?

    My pump has been running 24 hrs so everything should be stabilized now but the pool is still very cloudy. I did a retest today and got the following readings.

    FC =12 Also did the cheap OTO test and it was the darkest yellow I have ever seen it.
    CC = 0
    TA =180
    CH = 320
    SALT 2.9
    CYA=50 It's been cloudy all day yesterday and today

    I don't have the ability to test for TDS. Full service pool store is quite far away but I am going to try and get a sample there this week for a metals test. The pool was filled with trucked water about 8 years ago and I have been using well water to top it off ever since.
    20*40 Liner 2'-8' deep, Spill Over SPA, Electric Cover, Jandy Purelink (Aquapure & PDA), Hayward SP2610x15 (1.5HP Single Speed), Hayward H300 (Millavolt)

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    Richard320's Avatar
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    Re: Can old DPD powder show inaccurate high reading ?

    Quote Originally Posted by aswetich
    My pump has been running 24 hrs so everything should be stabilized now but the pool is still very cloudy. I did a retest today and got the following readings.

    FC =12 Also did the cheap OTO test and it was the darkest yellow I have ever seen it.
    CC = 0
    TA =180
    CH = 320
    SALT 2.9
    CYA=50 It's been cloudy all day yesterday and today

    I don't have the ability to test for TDS. Full service pool store is quite far away but I am going to try and get a sample there this week for a metals test. The pool was filled with trucked water about 8 years ago and I have been using well water to top it off ever since.
    Who cares what TDS is? Cloudy is usually algae.

    I'm just wondering if you didn't use the large sample (25 ml) but multiply for the small? (10 ml)
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
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    Re: Can old DPD powder show inaccurate high reading ?

    Just to be sure I don't have a algae problem I shocked the pool yesterday. Using the pool school criteria I brought my FC up to 24 yesterday morning based on the CYA level and brushed it. Before going to bed last night I confirmed the FC was at 24. and brushed it again. When testing this morning the level remained at 24 so I would expect there is not a algae issue. I can see the floor drains but it obviously not as clear as it should be. Could there be dead algae floating around clouding the pool ? I ordered some DE to ad to my sand filter but is there something else I should be doing ?
    20*40 Liner 2'-8' deep, Spill Over SPA, Electric Cover, Jandy Purelink (Aquapure & PDA), Hayward SP2610x15 (1.5HP Single Speed), Hayward H300 (Millavolt)

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    Re: Can old DPD powder show inaccurate high reading ?

    How are you testing? YOu should NOT have been able to hold 24 ppm FC during the day. Sunlight consumes FC.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Can old DPD powder show inaccurate high reading ?

    I was probably able to keep the FC up during the day because I live in Michigan and the weather can be all over the place. The day I shocked it was almost dark as night. The FC stayed constant throughout the night so doesn't that mean the Algae is likely dead ? I have been using the DPD test for years and am positive it is being done correctly.
    20*40 Liner 2'-8' deep, Spill Over SPA, Electric Cover, Jandy Purelink (Aquapure & PDA), Hayward SP2610x15 (1.5HP Single Speed), Hayward H300 (Millavolt)

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    Re: Can old DPD powder show inaccurate high reading ?

    I brought my FC up to 24 yesterday morning based on the CYA level and brushed it. Before going to bed last night I confirmed the FC was at 24.
    That's what doesn't work. You literally cannot go all day and not lose FC.....regardless of the weather.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    linen's Avatar
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    Re: Can old DPD powder show inaccurate high reading ?

    As duraleigh said, even with the conditions you listed, you should have lost some FC.

    Did you have the aquapure Saltwater chlorine generator (swg) off or on? We recommend not using the swg during the shock process (saves some cell life). In addition, when you do the OCLT, the swg needs to be off.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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