The 12-inch in diameter stainless steel Cool Coil COOLCOIL is designed to be used with a water chiller (sold seperately). The chilled fresh water is pumped through the coil which should be submerged in the Epicenter of the Under Current or any other hydroponic nutrient reservoir. The fresh water flowing through the Cool Coil from the chiller is used to cool the reservoir and does not mix with the water in the reservoir. With the Cool Coil, you don't have to worry about nutrient water contaminating your chiller. Includes 20-inch of 3/8 inch heavy duty tubing, 1/2 inch and 3/8 inch brass hose barb adapters, and stainless steel hose clamps.