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 Cascade Aquarium Heaters are factory set to 76 ℉, and are safe for either freshwater or saltwater fish tanks. The 25W model works great for fish tanks up to 5 gallons. 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 Cascade 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.