VITAL FOR ALL TANKS: Monitor tank temperature accurately - essential for healthy fish. Great 2" strip thermometer for smaller fish tanks. EASY TO USE Simply remove backing paper and apply to outer wall of aquarium. EASY TO READ: Thermal Paper indicates temperature in Fahrenheit (64 - 86 degrees) and Celsius (18 - 30 degrees). If two temperatures are indicated, the accurate water level is between those two. SHOP PENN-PLAX FOR ALL YOUR PET’S NEEDS: Penn-Plax is a manufacturer and distributer of top quality pet supplies, who specialize in creating excellent pet products for animals, both great and small.