Ozonators do sanitize water, but the process alone is insufficient for most bather loads. In most cases, the simple act of climbing into the water releases enough contaminants to overwhelm the ozonator's efforts for hours. This leaves the spa unsanitized while in use. Maintain a chemical residual, however, and the spa stays clean even after guests drop in. The hotter the hot tub, the cleaner it is.
Many germs love it hot.
The only thing scared away by a too hot tub is a sensitive bather. No matter the temperature, a hot tub's water must be balanced and sanitized. Foamy bubbles are a normal part of having a hot tub. Foam in a spa indicates that something is wrong with the water balance, as does greenness, sand, cloudiness, a noticeable smell and scum along the tile line. Properly treating hot tub water will eliminate the things that lead to foam, including body oils, soaps and excessive algaecides.