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Thread: Will liquid bleach lower the pH?

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    Will liquid bleach lower the pH?

    On Friday my pH was 8.0. I added bleach to the pool Friday night and again tonight and my pH is now 6.8.

    I'm going to add borax to bring it up. How long do I have to wait after adding borax before I can go in?

    Andy
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    Re: Will liquid bleach lower the pH?

    What is your TA? pH that swings around wildly following chemical additions is sometimes an indicator of a TA that is too low.

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    JasonLion's Avatar
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    Re: Will liquid bleach lower the pH?

    No, bleach will never lower the PH. Bleach is long term PH neutral or just slightly basic (raises PH). When you add bleach the PH goes up temporarily, and then as the chlorine gets consumed the PH goes down again. Some brands of bleach cause a noticeable net increase in the PH, but most are close to PH neutral.
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    Re: Will liquid bleach lower the pH?

    Shocked my pool with 10.5% last night and the PH went from 7.5 last night to 8.2 this morning with a TA of 100.
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    Re: Will liquid bleach lower the pH?

    Just to get this thread onto the right track, and repeating what Jason has said, the addition of bleach to a pool is a net ZERO on pH change.

    There are other variables at work (I don't know what) if your pH has changed concurrent with the application of bleach or liquid chlorine, but the bleach is not the cause of it.
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    Re: Will liquid bleach lower the pH?

    My PH was 7.5 at 9:00 pm, shocked my pool at 10:30, PH at 8:00 next morning was 8.2 with no other chemicals added it just made since that it was a result of additional clorine. jasonlion above indicated that some bleaches can increase PH so I am confused.
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    Re: Will liquid bleach lower the pH?

    Pool School's article on shocking doesn't mention pH, but the posts I've seen, including Jason's post above, indicate that the pH can go up temporarily while shocking, then goes back down when the FC is used up & returns to normal levels. I've also seen comments that the pH test is not valid during the high FC levels of shocking because it gives false high readings. Maybe someone else could clarify which one (or both) of those are valid - maybe the comments about false high pH readings are related to the temp pH rise?
    Andy
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    Re: Will liquid bleach lower the pH?

    Using bleach will raise pH, but only very slightly. This is due to excess lye in the bleach that is unavoidably formed during the manufacturing process. Stronger concentrations (like 10 or 12%) generally have more excess lye in them, but the affect still is small enough to generally be ignored.

    The false FC high at high pH is indeed a false high, not just a temporary high. It happens because high levels of chlorine convert the pH indicator dye from phenol red to chlorphenol red, which shows up as pink-red even at lower pH values. The indicator has some chlorine neutralizer in it to normally prevent this, but at high FC levels the neutralizer is overwhelmed.
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    Re: Will liquid bleach lower the pH?

    Thanks, The false high in the test makes sense to me now I will just have to see how the PH plays out as the FC comes down seeing how I added 2 quarts of MA to adjust it down this morning.
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    Re: Will liquid bleach lower the pH?

    It is both really. Very high FC levels will cause the PH to read higher than it actually is. And, the PH goes up temporarily when you shock with bleach.
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    Re: Will liquid bleach lower the pH?

    Quote Originally Posted by 257WbyMag
    What is your TA? pH that swings around wildly following chemical additions is sometimes an indicator of a TA that is too low.
    My TA was only 40. I added some baking soda and got it up to 100, which, of course, raised my pH. My FC is 3 ppm right now. But now it's raining, so I am sure my numbers will be all over the place when the rain stops.
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    Re: Will liquid bleach lower the pH?

    Would diluting the sample with tap water give you a general idea of where your PH might be? Like when you dilute your pool sample to measure high chlorine levels? I suspect it won't work, given PH is a logrithmic measurement, but I thought I would ask.

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    Re: Will liquid bleach lower the pH?

    Quote Originally Posted by maribrow
    Would diluting the sample with tap water give you a general idea of where your PH might be? Like when you dilute your pool sample to measure high chlorine levels? I suspect it won't work, given PH is a logrithmic measurement, but I thought I would ask.
    No. Calculating the pH of a mixture is not that simple.
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    Re: Will liquid bleach lower the pH?

    Quote Originally Posted by maribrow
    Would diluting the sample with tap water give you a general idea of where your PH might be? Like when you dilute your pool sample to measure high chlorine levels? I suspect it won't work, given PH is a logrithmic measurement, but I thought I would ask.
    You should also not use tap water for dilution for measuring chlorine unless you have non-chlorinated water.

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    Re: Will liquid bleach lower the pH?

    Quote Originally Posted by maribrow
    Would diluting the sample with tap water give you a general idea of where your PH might be? Like when you dilute your pool sample to measure high chlorine levels? I suspect it won't work, given PH is a logrithmic measurement, but I thought I would ask.
    Welcome to TFP!

    If you were to dilute the sample with distilled water (i.e. unbuffered water), then the pH would remain essentially unchanged because of the pH buffering from the sample but other parameters such as FC would get cut down. So in theory one could dilute the water so that the FC were lower and no longer chlorinating the phenol red dye in the pH test.

    If the pH is so low or high as to be off scale, then you can't dilute it to bring it into range (except by using buffered water such as tap water, but that gets complicated). What you can do, however, is use acid demand or base demand reagent to move the pH, but to figure out the original pH requires knowing the TA and other buffering parameters and is complicated. Usually, it doesn't matter since you just need to get the pH into proper range.
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    Re: Will liquid bleach lower the pH?

    Thanks all - this is a great forum. Wish I found it before I trichor'd my CYA up to 120 and spent a ton of $ on algae killing products and phophate removers.

    I am using a Taylor K1004 DPD test kit, and I got a false reading for PH for the first time yesterday a few hours after I added Bleach to my pool to bring up my FC, and then I added a pint of MA to bring down the PH before I read this thread

    Today, my readings are:
    FC > 25
    CYA 120
    TA 100
    PH 7.5
    13,000 gal plaster inground pool.

    My reagent is Taylor R-0014, should I trust the PH reading given my FC is > 25? (I used distilled water this time for my 1:4 dilluted test sample)

    I'll be getting my pool replastered in the next few months, so I'm holding off draining my pool water and want to try to keep the algae away, but not ruin any pool equipment!

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    Re: Will liquid bleach lower the pH?

    Quote Originally Posted by maribrow
    My reagent is Taylor R-0014, should I trust the PH reading given my FC is > 25? (I used distilled water this time for my 1:4 dilluted test sample)
    No. The pH reading is falsely high when the FC > 10ppm.
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    Re: Will liquid bleach lower the pH?

    Quote Originally Posted by maribrow
    Thanks all - this is a great forum. Wish I found it before I trichor'd my CYA up to 120 and spent a ton of $ on algae killing products and phophate removers.

    I am using a Taylor K1004 DPD test kit, and I got a false reading for PH for the first time yesterday a few hours after I added Bleach to my pool to bring up my FC, and then I added a pint of MA to bring down the PH before I read this thread

    Today, my readings are:
    FC > 25
    CYA 120
    TA 100
    PH 7.5
    13,000 gal plaster inground pool.

    My reagent is Taylor R-0014, should I trust the PH reading given my FC is > 25? (I used distilled water this time for my 1:4 dilluted test sample)

    I'll be getting my pool replastered in the next few months, so I'm holding off draining my pool water and want to try to keep the algae away, but not ruin any pool equipment!
    If you read the pH very fast it might be OK @ more than 10 but 25 is pushing things.

    When shocking the pH is actually high but will drop as the FC drops it also reads higher than it is. Per chem geek this is not as much of a problem with the maintenance FC over 10 that would be needed with a high CYA.

    I would just try to track the pH as the FC falls and adjust only if the pH appears to drop below 7.2...


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