Chlorine demand is defined as ‘the inability to maintain a chlorine residual in a pool or spa’ even after repeated application of a chlorinating product. It is one of the most frustrating problems a pool owner can experience, as continued application of product seems to make no difference in water quality or in the ability to maintain a sanitizer residual. Pool and Spa Marketing https://www.poolspamarketing.com/trade/how-to-prevent-and-treat-depleted-sanitizer-levels-in-pool-water/print/