Marina Floating Thermometer with Suction Cup. With water temperature being such a critical factor for the well-being of fish, it’s important to have a good thermometer. This Marina Floating Thermometer is designed to float in the water in a vertical position. It comes with a suction cup for optional installation on your aquarium glass. Accurate and easy to read, it provides temperature readings in Centigrade and Fahrenheit. It also has a safety zone temperature range indicator for most tropical fish. For fresh or saltwater aquariums.