As mentioned above, oxidizing chemicals come in a concentrated form called shock, which is used to supersanitize spa water. In addition to regenerating bromine, shocking burns up bacteria, algae, nitrogen compounds, and smelly ammonia that have not been removed through routine sanitization. Maintaining the proper sanitizer residual will keep your spa safe for bathing, but shocking the water is sometimes necessary to remove dead bacteria and organic matter that could cause skin and eye irritation, cloudy water, and foul odors.
The best time to shock your spa is after sundown, which eliminates the dissipating effect of the sun’s ultraviolet rays, or after heavy use. Some shocks, such as chlorine, require bathers to wait until the residual has dropped below 10 ppm before getting in the water. Others, such as monopersulfate, simply regenerate the bromine already in the water, so there is no need to wait before entering the spa. Before adding a spa shock, however, always bring the water balance factors into their proper ranges.