Enjoy softer, cleaner spa water naturally. Watkins MFG's new AG PLUS contains natural minerals known to control bacteria and prevent algae. Can be with all sanitizing systems including bromine, chlorine, or ozone, and non-chlorine shock. Simply insert the purifier cartridge into your spa filter. When used with a minimal sanitizer residual of 0.5 ppm, the AG Plus will allow you to enjoy naturally clear water for up to 4 months!