The Nature 2 Spa Mineral Sanitizer and Test Strip pack is a great value and a convenient way to keep your spa water properly sanitized while ensuring accurate water chemistry. Nature 2 Spa Mineral Sanitizer cartridges use patented mineral bed technology to reduce the amount of bromine needed to sanitize your spa or hot tub. These mineral cartridges work with your existing filtration system and are installed directly into your filter. Each mineral cartridge lasts up to four months and gives you fresh, clean spa water without the strong smell and harsh side effects of traditional chemicals. Nature 2 Spa Test Strips are an easy and reliable way to measure levels of MPS, alkalinity and pH in your hot tub. This item includes four Nature 2 Spa Mineral Sanitizer Cartridges and one package of Nature 2 Spa Test Strips.