This SpaRX Mineral Sanitizer is designed for chlorine treated spas up to 400 gallons. This mineral based purification system is an easy and safe way to significantly reduce chemical use in your spa while providing outstanding water quality. The rod contained in the floating cage is loaded with zinc, silver and heavily isolated copper to kill contaminants and algae while making your water noticeably softer. Simply drop the SpaRX cage into the skimmer or between filter cartridges and let it go to work for you. Replace the SpaRX mineral rod every four to six months to keep your spa healthy and clean.