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?