pH is a measure of how acidic or alkaline a substance is and has a scale ranging from 0 – 14, with 7.0 being neutral. Water with a pH below 7.0 is acidic and above 7.0 is alkaline. For spas, the ideal level is 7.5 which, being slightly alkaline, protects the spa finish and equipment from corrosion and provides optimum bather comfort as this is the same pH as most mains tap water. SpaGuard Lo n Slo is used to lower the pH when the level rises above the ideal range of 7.4 - 7.6.