An aquarium water chiller will lower and maintain safe aquarium temperature. An external chiller has plumbing fittings. Many hobbyists plumb the chiller in line with the return pump or add a small feed pump dedicated to the chiller. In addition to the chiller and pump, you will need tubing and hose clamps, and sometimes an aquarium temperature controller. Be sure your fish tank cooler is well ventilated, and that the water flow rate is correct to ensure efficient performance and long life.