Floating Glass Thermometers deliver accurate and easy-to-read temperature measurements in home or commercial aquariums. The unique floating design is equipped with a strong suction cup. Either secure the thermometer to the side of the tank in a convenient location or allow it to float freely on top of the water for a better picture of tank temperature in a variety of locations. The clear glass thermometer displays temperatures in both Celsius and Fahrenheit for international use. The thermometer is suitable for use in freshwater or saltwater tanks. Underwater Treasures Floating Glass Thermometers are mercury free for fish safety. The thermometers measure 4.5 inches in length and include a green-band on the temperature line to indicate the correct aquarium water temperature for optimal fish comfort and health. The glass thermometer can be cleaned as needed and the smooth glass surface resists fogging and algae growth. Underwater Treasures Floating Glass Thermometers require no batteries or special equipment to operate and are guaranteed to be accurate.