The HOC replacement filter is used for Sprite's Universal High Output filter systems. This filter removes chlorine, hardness, and scale buildup from shower water, and lasts for approximately 12 months or 25, 000 Gallons of water. Sprite High Output Shower Head Replacement Chlorine Filter Replacement Filter for The Sprite High Output Massaging Shower Housing 2 3/4-Inch Wide By 2 1/2-Inch In Diameter each Filter Lasts Approximately Six Months