This heater easily maintains healthy water temperature within a 1° accuracy, and can be set anywhere between 68 ℉ and 89 ℉, by using the red control knob. Our Aquarium Heaters are factory set to 76 ℉, and are safe for either freshwater or saltwater fish tanks. The 100W model works great for 15 - 20 gallon tanks. Visible & Accurate Temperature Scale: With an easy to read setting scale in both Celsius and Fahrenheit, it's easy to see the temperature adjustments being made. To increase the temperature, rotate the control knob counter-clockwise, and to decrease, rotate it clockwise; or, follow the + and - symbols located near the control knob. Orange Pilot Light: Our Heat Aquarium Heaters feature a pilot light that indicates the heating cycle status. This means that it will go on and off by itself as the thermostat cycles the heating element on and off. In other words, orange light = heater is on. Similarly, these aquarium heaters make a faint click when turning off. Additional Features: In addition to being composed of heavy-duty and shock-resistant glass, these fully submersible aquarium heaters can be placed either horizontally or vertically. There's also a built-in minimum water level indicator at the top, colored in red. Please Note: Do not operate heater outside of aquarium, and never submerse a hot heater into an aquarium - only submerse a cool heater. After placing the heater into your aquarium, wait 15 minutes before turning on. This allows the thermostat to adjust itself to water temperature. Measurements: Overall Length = 8.5" / Overall Diameter = 1.1" / Suction Cup Diameter = 1.25" / Wattage = 100W / Voltage = 110V.
