Centigrade and Fahrenheit - With Suction Cup - For fresh and salt water - Accurate and easy to read - Safety zone indicator for most tropical fish - Protects fish from unsafe temperatures The MARINA floating thermometer with suction cup is accurate and easy to read, it has a safety zone indicator for most tropical fish. Protect your fish from unsafe temperatures. Simply suction thermometer in the aquarium and you are ready to go. For fresh or saltwater aquariums. Info from Hagen