Warm Tone Aquarium Heater Fully submersible aquarium heater with a digital LED temperature display. The Penn-Plax warmtone LED display heater accurately sets and maintains the temperature in your fish tank. The temperature ranges from 61 to 90 degrees Fahrenheit, with a reliable, sensitive, and precise temperature adjustment dial. The LED display heater is fully submersible and can be placed horizontally or vertically in your freshwater or marine water tank. The heater is enclosed in a high quality quartz tube to protect the top quality electrical components.