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Thread: Staining w/ conflicting PH readings

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    Join Date
    Aug 2013
    Location
    Rochester, NY
    Posts
    12

    Staining w/ conflicting PH readings

    Hi all,

    Current test readings from my TF-100:

    FC: 6.5
    CC: 0
    PH: 7.4
    TA: 40
    CH: 150
    CYA: 30

    I opened my pool this year to pure green - quickly shocked and filtered 24/7 and now water is crystal clear.

    I have some brownish staining in my deep end (along the ridges where it grades up towards the walls). I also have some very slight yellow discoloration along the pool bottom edges. Thinking they were organic, I followed SLAM method and passed OCLT. Staining remains, letting my FC drop to normal levels today.

    I decided to bring my water to my local large pool store to have it tested for metals. 0 metals, phosphates around 200 (they said nothing to worry about, and it rained today.. who cares about phosphates anyway). The weird thing is that their testing mirrored the results from my TF-100, except PH which they measured at 8.2! The guy told me I was getting an inaccurate PH reading on my test-kit because my FC was so high (6.5.. not that high right?) and that their test will allow them to test PH at all FC levels, therefore accurate.

    Came back home and tested PH again with two separate test kits.. both times 7.4. What the heck. Can I get false low PH readings with high FC? I thought I could only get false highs.

    Anyway - I added some baking soda to get my TA up (hopefully just to 60). I know high PH can constribute to staining.. should I try some dry acid?

    Thanks guys - this is a wonderful resource to pool owners!

    Ross
    32 x 16 Vinyl
    Pentair Sand Dollar SD-60 Sand Filter
    Pentair Superflo (1.0 HP)

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    Apr 2007
    Location
    Sebring, Florida
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    Re: Staining w/ conflicting PH readings

    Hey, Ross,
    Came back home and tested PH again with two separate test kits.. both times 7.4. What the heck. Can I get false low PH readings with high FC? I thought I could only get false highs.
    It's just more pool store bogus garbage. They make stuff up. Stay out of the pool store.

    The pH test in the TF-100 begins to read falsely high around 10 ppm chlorine and above. Now that doesn't mean it reads 7.4 at 9.5 ppm and pH 9.9 at 10 ppm.....it's just slightly higher. For the pool store to tell you you are wrong at 6.5 ppm is laughable......he has to make up something instead of admitting their test is kiltered......badly.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Join Date
    Aug 2013
    Location
    Rochester, NY
    Posts
    12

    Re: Staining w/ conflicting PH readings

    Thanks for the quick reply - that is kind of what I expected.

    Any thoughts on what my staining could be? I should mention that I've tried vitamin c tablets and they really don't do anything. They would diminish both iron and rust , correct?

    My only other thoughts are:

    - organic from large amounts of leaves in the pool over the winter... But maintaining shock levels hasn't helped.

    - poor circulation and FC not reaching these areas .. My main drain doesn't seem to be working well.

    - my low TA causing ph fluctuation which is causing stains?

    Any of the above plausible?

    Thanks again!

  4. Back To Top    #4

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

    Re: Staining w/ conflicting PH readings

    Identify the stain as organic or inorganic. Seems like the vitamin C had no affect so take a puck and hold it onto the stain for a couple of minutes. If it lightens the stain, the stain is organic and chlorine is the answer.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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