The Nature2 Mineral Purifier is a purifier cartridge that slips inside the spas filter and last four months. It assists the sanitizer by reducing the amount of sanitizer required to keep the spa clean. Use in conjunction with bromine or chlorine, and a non-chlorine MPS shock. When using the Nature2 Mineral purifier you can safely reduce the bromine level from 3ppm to 0.5pp. It will dramatically reduce the amount of bromine sanitizer needed to keep the spa water clean and clear. As water is filtered it flows through the Nature2 purifier cartridge, where a non-electrical reaction takes place that "activates" oxygen to kill bacteria, algae, and viruses. Compatible with ozone and bromine. Assures an odor-free spa. Significantly improves look & feel of water. Simplifies water balance — it's unaffected by heat. Lasts four months.