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Thread: Sulphuric Acid as the primary pH control chemical

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    Sulphuric Acid as the primary pH control chemical

    Hi,
    We are seeing a large shift in Australian Commercial Pools away from sodium hypochlorite (which has been practically regulated out of the new pool market by requirements of the Australian Standards) to calcium hypochlorite dosing systems such as Granudos. These systems utilise sulphuric acid (35%) internally for scale control, and have the capacity to be used for the addition of sulphuric acid for pH control. We are seeing more pools where this is occurring, and can understand the attraction of having fewer different chemicals required to operate the system. Can the continued use of sulphuric acid lead to formation of sulphate in the pool water environment? We sometimes come across acid sulphate soils which require alternative concrete mix design to resist the sulphate attack and can see the possibility of sulphate in the pool water carrying out similar attack to the wet deck channels and balance tank which are normally an exposed concrete finish. This paper recommends that sulphate in water that is in contact with concrete be restricted to a maximum of 150ppm, and if potentially exceeded, then the concrete mix used should be designed for the sulphate application. PWTAG recommend a maximum of 300ppm so both are within the same ballpark at least. The links and information in the TFP thread focus on sodium bisulphate as a problem rather than sulphuric acid, so perhaps we are unnecessarily concerned, however other threads indicate that sulphuric acid does cause sulphates in the water and as such should not be used exclusively for pH control.
    Has anyone seen an incident where exclusive use of sulphuric acid for pH control has caused an increase in pool water sulphate levels toward or above the 150-300ppm limits given above?

    Rob

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    JasonLion's Avatar
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    Re: Sulphuric Acid as the primary pH control chemical

    Welcome to TFP!

    Small, or even medium, amounts of sulfates are not a big deal, but large quantities can be a real problem.

    Nearly everyone uses muriatic acid instead, so I haven't come across any recent examples of problems, just because the situation is incredibly rare.
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    Patrick_B's Avatar
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    Re: Sulphuric Acid as the primary pH control chemical

    H2so4 is used almost exclusively in the industrial cooling water arena, and the only reason there are no Sulphate issues is that these systems are constantly replenished with new water. I would think in pools, it would lead to big problems sooner rather than later.
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    bobodaclown's Avatar
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    Re: Sulphuric Acid as the primary pH control chemical

    When I first got my pool, went to one of the local pool installers, they used Sulphuric Acid to lower pH. Didn't want to add sulphate to the pool. There are lots of theads here on the forums: https://www.google.com/search?q=Sulp...lefreepool.com
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    Re: Sulphuric Acid as the primary pH control chemical

    See Sulfates why so bad? and Sulfates - what's the problem?.

    Why is Australia moving away from sodium hypochlorite? What is the problem they see with it? Cal-Hypo has issues with fire in storage unless it's less than 50% in concentration. See National Fire Protection Association (NFPA) Ratings.
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    Re: Sulphuric Acid as the primary pH control chemical

    The Australian Standard for corrosive substances was updated in around 2008 to include a requirement for the truck delivering the hypo to be in a contained area when transferring hypo to the sites storage tank. On the face of it, this doesn't appear to be a problem, but dealing with rainfall complicates things a great deal, in fact, I have not yet seen a site where this has been adequately addressed. We normally specify cal hypo and either hydrochloric or CO2 to avoid the difficulties of dealing with hypo. But as noted in the OP, the cal hypo feeder uses sulphuric acid for its cleaning process.

    Rob.

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    Re: Sulphuric Acid as the primary pH control chemical

    For every 10 ppm Free Chlorine (FC) added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

    So if the sulphuric acid is only used for cleaning and not for pH control, then the amount may be manageable and not build up too much sulfates.
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