It is made available for hot tubs and spas through the use of a device called an Ozonator.
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.