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Thread: PH readings fluctuate

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    PH readings fluctuate

    For the first time in 8 years, my pool PH is varying wildly. Usually in Texas in August, the PH gradually goes up and I add acid about once a week. Now, the PH will read 7.7 one day and 6.9 the next day. I retake it in a different part of the pool, and it reads 7.9.
    I have to take it several times and finally decide based on several different reading whether to add acid or not.
    I have two testing kits and they both seem to read the same.
    Is there a reason that the PH could go down to 6.9 overnight?
    Our pool is 20,000 gallons, temp. 86, Chlorine 6 (I use bleach), Total Alk 60, Calcium 300, CYA 50, plaster pool.
    Thanks,
    Barb
    20,000 gal white plaster, w/spa waterfall, DE filter

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    Mod Squad jblizzle's Avatar
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    Re: PH readings fluctuate

    Only if you are dumping in a lot of acid overnight.
    Jason, TFP Moderator
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    Re: PH readings fluctuate

    No acid overnight. I keep thinking the test kit is wrong somehow but I have 2 that read the same.
    20,000 gal white plaster, w/spa waterfall, DE filter

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    JesseSchmidt's Avatar
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    Re: PH readings fluctuate

    Are you testing after the pump has been running for a while? How old is the pool? I have read that plaster requires acid when it's new but have no experience as my pool is vinyl.
    26k Gal IG vinyl, Hayward Super 1HP, Hayward Pro Series S244T Sand Filter, TFTestkits TF-100 w/ Speedstir
    Links: TFPC for Beginners / ABCs of Pool Water Chemistry / GETTING STARTED / PoolMath / SLAM / TFTestkits / Chlorine/CYA Chart

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    Re: PH readings fluctuate

    And i get different reading at the same time of day just in different part of the pool.
    20,000 gal white plaster, w/spa waterfall, DE filter

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    Re: PH readings fluctuate

    Quote Originally Posted by JesseSchmidt View Post
    Are you testing after the pump has been running for a while? How old is the pool? I have read that plaster requires acid when it's new but have no experience as my pool is vinyl.
    After 8 years, plaster shouldn't really be affecting pH much any more - and if it were, it would be pushing it up, not allowing it to fluctuate.

    The other question is extremely important jkbk - are you testing after the pump has been running for a while?
    Also, what do your returns look like - I'm wondering if maybe there are dead spots in the pool.
    Finally - what happens when you test in the same exact place, same time, every day (assuming the pump has been on for a while)? Are you still getting fluctuations?

    TA is 60, I wouldn't think a TA that is too low could be causing a problem, but you could also try using PoolMath to raise TA to 80 and see if it stabilizes.
    8,500gal plaster in-ground with attached spa, two floor drains, one skimmer. Chlorine, City Water.
    Pentair WhisperFlo 1hp Pump, MagnaTek Midcentury EPlus motor, Pentair CleanNClear 200SF Cartridge filter, Purex Triton MiniMax 250 Gas Heater, Pentair SunLite, AutoFill.
    Kreepy Krauly Cruiser, TF-100 with SpeedStir. :D

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    Re: PH readings fluctuate

    What test kits are you using and how old are they? Do you store your kits inside? Heat and sunlight degrade the reagents.
    Karen
    33K IG w spa plaster, Pentair 1HP Whisperflo, DE Filter, SWG CircuPool RJ-60, Dolphin Triton Plus, Raypak Dig 336K BTU, TF-100.
    Pool Math Chlorine / CYA Chart SLAM - Shock Level And Maintain
    2017 replaster/retile

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    Re: PH readings fluctuate

    Test kit is new. I do test in the same spot with the same weird results but now I test 3 times around the pool. 1 will be low, 2 will be high�� I will bring up TA and see if it helps. The pump runs at least 3 hours before testing. Our pool is 16 years old... Original plaster.
    20,000 gal white plaster, w/spa waterfall, DE filter

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    Re: PH readings fluctuate

    It's fascinating that your pH fluctuates that heavily.

    I'm back to either:

    1. The returns are misaimed, creating "dead" spots where the chemicals aren't mixing in.
    2. (More Unlikely) - The TA is too low for your particular situation, causing pH flux.

    Honestly, wait for an expert to chime in, no worries! We'll help you get it figured out, but you unfortunately have an "interesting" situation.
    8,500gal plaster in-ground with attached spa, two floor drains, one skimmer. Chlorine, City Water.
    Pentair WhisperFlo 1hp Pump, MagnaTek Midcentury EPlus motor, Pentair CleanNClear 200SF Cartridge filter, Purex Triton MiniMax 250 Gas Heater, Pentair SunLite, AutoFill.
    Kreepy Krauly Cruiser, TF-100 with SpeedStir. :D

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    Re: PH readings fluctuate

    What test kits are you using?


    Karen
    33K IG w spa plaster, Pentair 1HP Whisperflo, DE Filter, SWG CircuPool RJ-60, Dolphin Triton Plus, Raypak Dig 336K BTU, TF-100.
    Pool Math Chlorine / CYA Chart SLAM - Shock Level And Maintain
    2017 replaster/retile

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    Mod Squad pooldv's Avatar
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    Re: PH readings fluctuate

    Quote Originally Posted by kcindc View Post
    What test kits are you using?
    Ditto.
    TFP Moderator
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    Re: PH readings fluctuate

    Taylor Basic residential pool & spa k-1000

    Happened again today. First reading 6.9. Next 4 readings all 7.6
    20,000 gal white plaster, w/spa waterfall, DE filter

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    Mod Squad jblizzle's Avatar
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    Re: PH readings fluctuate

    Sounds like your container was not clean for the first test.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
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    Re: PH readings fluctuate

    I hope you also have the Taylor K-2006 or the TF-100 to test your other chem levels. Pool School - Test Kits Compared

    Extended test kit directions, scroll down to the PH test: Extended Test Kit Directions
    Karen
    33K IG w spa plaster, Pentair 1HP Whisperflo, DE Filter, SWG CircuPool RJ-60, Dolphin Triton Plus, Raypak Dig 336K BTU, TF-100.
    Pool Math Chlorine / CYA Chart SLAM - Shock Level And Maintain
    2017 replaster/retile

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