Penn Plax offers a variety of different styles of Aquarium Thermometers. Aquarium Thermometers are an important component for every aquarium set-up. The provide clear, accurate live temperature readings of your aquarium water's temperature, allowing the aquarium hobbyist to fine tune their heating system to provide the appropriate water temperature for their fish. Multi-use economical Thermometer. Comes with suction cup. 4.25""H.