Ozone is often used in spas and pools to help reduce contaminants. Used by itself, it is inadequate for eliminating bacteria. However, used in conjunction with chlorine or bromine, an ozonator can effectively eliminate enough bather contamination to allow less chlorine to be tied up in the form of chloramines and more to be free and available to kill bacteria.
Ozone can reduce the amount of chlorine used, but the free chlorine level should still be kept at least at 1.5 ppm. Shocking will still be necessary also, as ozonators do not completely eliminate the gradual build-up of waste in the water.