High Quality :Using Quartz Explosion-proof Glass, Strong and Corrosion-resistant, Automatic Constant Temperature, Automatic Power Off When Over 36C/96F Built-in Temperature Sensor: the Water Temperature Can Be Accurately Displayed on the External Controller in Real Time, and the Temperature Adjustment Range Can Be Set Arbitrarily From 18C to 34C (64F to 93F). When the Water Temperature Is Lower Than the Set Temperature, the Fish Tank Heater Will Automatically Start Heating Keep the Water Temperature Constant Until the Water Temperature Reaches the Set Temperature Automatic Constant Temperature:Using External Control Electronic Temperature Regulation, Intelligent Frequency Conversion Technology, High Heating Efficiency, 3-digit Display to Accurately Control Temperature, Adjustment Accuracy 0.5 / 1. The heater's working frequency will be changed according to temperature variation, and the heating is automatically stopped when the set temperature is reached. Super Mini Size: Compact design, take less space in the fish tank, easy to hide in the tank.10W Is Suitable for 1-3L/0.26-0.79 Gallons Fish Tank, Power 20W Is Suitable for 4-6L/1.06-1.59 Gallons Fish Tank; Power 30W Is Suitable for About 8L/2 Gallons Fish Tank Daily maintenance: The suction cups must be cleaned every month to prevent the heater from falling off and breaking because the suction force is weakened by stains.