Ozone is formed when three atoms of oxygen are bound together, instead of the normal two. Mother Nature makes it naturally, if you have ever detected a faint, sweet smell in the air after a lightening storm, that was Ozone. Ozone not only destroys microorganisms, it also breaks down harmful chemicals and causes total dissolved solids to clump together for easier removal by the filter. Ozone also oxidizes combined chlorine and bromine, freeing them to be continuously reused. The result is water that is cleaner, clearer, and smoother feeling to the skin.
Ozone helps prevent the calcium in spa water from chelating, and thus conditions the water.
This is good for equipment and more enjoyable to you. You will still need to use a system chemical such as bromine, chlorine as a sanitizer. Plus you spa experience will be heighten by less work, and less harsh chemicals to burn you eyes, nose and skin. To be effective, you should run your ozonator at least 4-6 hours per day. Continuous is best.