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Thread: Can’t I just lower my PH by adding some muriatic acid?

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    Can’t I just lower my PH by adding some muriatic acid?

    I am fighting an algae problem. I am keeping my water chemistry in check. My local pool store is telling me that a lower PH will allow the chlorine to be at a higher level, is that true? Here is what they are telling me.
    Active Chlorine pH
    97% 6.0
    91% 6.5
    76% 7.0
    66% 7.2
    50% 7.5

    I do not plan on swimming any time soon and it is going to rain all weekend. Can’t I just lower my PH by adding some muriatic acid?

    Won't this help me fight the algae better?

    Thanks in advance.
    14K gal gunite pool
    A.O. Smith B130 2.4hp motor
    Hayward DE2420L Filter
    Hayward SP3020X25AZ Super II Pump 2 1/2 HP Single Speed
    Aqualink rs4
    AutoClear salt system

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    JasonLion's Avatar
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    Re: Can’t I just lower my PH by adding some muriatic acid?

    Those numbers are only true when your don't have any CYA in the water. When you are using CYA, the active chlorine level mostly has to do with the CYA level, and only changes a little bit as the PH changes. The change with PH is small enough that you can just ignore it as long as your PH is in the normal range. When PH is way out of range there can still be some issues.
    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’t I just lower my PH by adding some muriatic acid?

    Muriatic acid is the preferred way to lower pH. Before you do this though, post your test results for your pool water so we can see where you're at.

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    Ohm_Boy's Avatar
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    Re: Can’t I just lower my PH by adding some muriatic acid?

    And, you do not want your ph to drop below 7.0
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

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    Re: Can’t I just lower my PH by adding some muriatic acid?

    Why not drop ph below 7.0 if your not going to be in the water and you know there is rain?

    What harm will it do?
    14K gal gunite pool
    A.O. Smith B130 2.4hp motor
    Hayward DE2420L Filter
    Hayward SP3020X25AZ Super II Pump 2 1/2 HP Single Speed
    Aqualink rs4
    AutoClear salt system

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    JasonLion's Avatar
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    Re: Can’t I just lower my PH by adding some muriatic acid?

    It depends on what kind of pool and equipment you have. Vinyl can be damaged by long term exposure to PH below 7.0. Copper heat exchange coils in most pool heaters can also be damaged below 7.0. Plaster pools can be damaged by a combination of low PH, low TA, and low CH, so low PH may or may not cause problems depending on your other levels. Fiberglass is also at some risk, though PH needs to be lower than that before there are problems.

    Also, you don't want to swim when PH is below 7.2.
    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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    Aquatica's Avatar
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    Re: Can’t I just lower my PH by adding some muriatic acid?

    drop the pH with acid. down to 7.2-7.4 appearently chlorine is more affective at lower pH levels. not sure how much more but it is a good idea not to have high pH when shocking.

    FC shock will kill algae. make sure its enough..depends on CYA level. bleach is the best method although the more expensive shock than say calhypo which is cheaper but leave residue and can cause other problems..so best use bleach..generic.unscented. so basicallt drop pH with acid then shock, backwash, shock until clear.

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