It is important to have the correct concentration of free available chlorine in the water at all times when the pool or spa is available for use. Unlike combined chlorine, free available chlorine is efficient at destroying the majority of harmful microorganisms. A minimum of 1.0 ppm free available chlorine is required if cyanuric acid is not used as a conditioner. Otherwise, a minimum free chlorine residual of 1.5 ppm is required. The maximum concentration of free available chlorine must not exceed 10 ppm while the pool is available for use. Chlorine must be dispensed through a properly-sized automatic chlorinator to ensure consistent levels of chlorine.