Nature 2 Spa Mineral Sanitizer cartridges significantly reduce the need for bromine while providing powerful sanitation for your spa or hot tub. Available for spas up to 500 gallons, these cartridges are placed in your spa filter and work with your existing system to provide you with the ultimate in hassle-free maintenance. These mineral sanitizer cartridges last up to four months and use an EPA approved patented mineral bed technology to give you a fresh, clean spa without the irritating side effects of traditional chemicals. This item includes three Nature 2 Spa Mineral Sanitizer Cartridges.