The Penn Plax Cascade 100 Watt Submersible Heater is for Aquariums up to 20 Gallons. Automatically sets and maintains to your desired temperature, and is accurate to one degree. The Cascade Submersible Heater contains easy view on/off light, dual suction cups with mounting clip and visible and accurate temperature setting scale. Constructed of heavy duty and shock resistant glass. This is a top quality heating element with superior insulation and heat distribution, perfect for fresh and salt water aquariums.