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Thread: bad acid or bad test?

  1. Back To Top    #1

    Join Date
    Oct 2016
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    NW Georgia
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    bad acid or bad test?

    Hello,

    I have a 900 gallon vinyl AGP - new set up.

    I added water, bleach, and CYA.
    Pump on for 48 hours, and the CYA is 40 with FC of 4. Excellent.
    I added borax and muriatic acid.
    Pump on for 48 hours, and the borates are 50 with a pH of 8.0. TA was 110-120.
    So I added 8 liquid ounces from a measuring cup of 31.45% muriatic acid.
    Pump on for 48 hours and retest. TA is still 110-120 with pH of 7.4

    I'm using HDX brand 5-way drop test. I know it can be hard to discern the shades of yellow for FC, but it was immediately available to at least get the pool started.
    Since the pH came down, it makes me think the acid did something.
    Could the acid be old or could the test be way off for TA - or something else?

  2. Back To Top    #2
    Mod Squad YippeeSkippy's Avatar
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    Re: bad acid or bad test?

    Actually, you may have this idea backwards. When your FC is higher than 10ppm, it can skew pH tests and make the pH appear higher (usually) than it actually is.

    Can you provide us with a full set of results:
    FC
    CC
    pH
    TA
    CH
    CYA

    Maddie
    Maddie :) 12K Fiberglass IG, Infinity 4000 automatic cover, SWCG, Hayward Sand Filter, Hayward 1.5 Pump, Doheny Discovery Robot, Savi Melody LED pool lights, outdoor speakers and other assorted doo-dads. Sundance Altamar Hot Tub.
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  3. Back To Top    #3

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    Re: bad acid or bad test?

    Quote Originally Posted by YippeeSkippy View Post
    Actually, you may have this idea backwards. When your FC is higher than 10ppm, it can skew pH tests and make the pH appear higher (usually) than it actually is.
    FC has never been higher than 5. It's a new set-up.

    FC - 4
    CC - 4
    pH - 7.4
    TA - 110-120
    CH - didn't test
    CYA - 40
    Borates - 50

    My question is why would TA stay at 110-120 despite adding enough muriatic acid to drop the pH?
    I didn't test pH immediately after adding acid. I added enough muriatic acid according to pool math to bring my pH down to 7.0 and then was aerating via the pump return for the past 48 hours.

    (ETA borates)
    900 gallon AG filled on 5/6/2017
    cartidge filter
    GA mountains
    BBB method

  4. Back To Top    #4

    Re: bad acid or bad test?

    Are you sure about the volume of the pool?

    The TA test can be +/- 10 ppm under good conditions, so it could be within the precision of the test when accounting for test variability.
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  5. Back To Top    #5

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    Re: bad acid or bad test?

    It's an easy set pool so it's narrower at the top than at the bottom. Intex specifications for 80% capacity and pool volume calculator by measurements are both pretty darn close to 900 gallons, so I'm going with it.

    So let's say the high TA reading was 120 and the low TA reading was 110.
    Shouldn't dropping the pH from 8.0 down to 7.0 do more than change TA by 10ppm?
    900 gallon AG filled on 5/6/2017
    cartidge filter
    GA mountains
    BBB method

  6. Back To Top    #6

    Re: bad acid or bad test?

    If the acid label says 31.45% muriatic acid, then it’s probably good. I wouldn’t be overly concerned unless you use the acid several times with no TA drop.

    Make sure that you’re doing the TA test the same each time. Hold the bottle vertically, wipe the tip if the drops seem off size, make sure that the sample volume is the same and allow for some change if fresh water is added.

    What’s your fill water TA?
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  7. Back To Top    #7

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    Re: bad acid or bad test?

    Fill water has a TA of 70-80
    900 gallon AG filled on 5/6/2017
    cartidge filter
    GA mountains
    BBB method

  8. Back To Top    #8

    Re: bad acid or bad test?

    Ok, at this point, I wouldn't be too concerned about the results.

    How will you be chlorinating?
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  9. Back To Top    #9

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    Re: bad acid or bad test?

    8.25% bleach
    900 gallon AG filled on 5/6/2017
    cartidge filter
    GA mountains
    BBB method

  10. Back To Top    #10

    Re: bad acid or bad test?

    What's your calcium hardness?
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