"Chlorine dioxide is destroyed by UV light. Care should be taken to apply it in conditions where it will not be exposed to sunlight. For example, it can be added to an outdoor pool or fountain at dusk and allowed to circulate overnight. Chlorine dioxide is readily stripped from water by contact with air. This can be minimized by adding Solution 3000 to a water system in which the recirculating pumps are running, but fountains, bubblers, waterfalls, etc. are turned off for extended periods (perhaps overnight) after adding Solution 3000."