Hydrolife Pre Fill Spa Filter is designed to be used on your water source as you fill or top-off your spa. The filter media effectively reduces levels of Calcium in source water, heavy metals, chlorine, chloramines and volatile organic compounds, which helps make balancing chemicals easier. It also pre-filters stain causing metals like iron, copper and manganese before they have a chance to damage your pool or spa. This easy-to-use filter connects to any standard garden hose and filters up to 2,500 gallons of water, depending on the quality of the water.