Description: SMALL FISH TANK HEATER: Specially designed for small fish tanks less than 1 gallon, does not occupy the space of the fish tank, USB power, rated voltage DC 5V. INTELLIGENT AND PRECISE CONSTANT TEMPERATURE: USB heating rod, the temperature can be adjusted from 15-34 degrees, When the water temperature is 0.1 ° lower than the set temperature, it enters the temperature control state OVERHEATING PROTECTION: When the water temperature exceeds 36 °C, display HH and indicator light will turn yellow, until the temperature returns below 34 °C, and the normal operating will resume. EXTERNAL CONTROLLER: External temperature controller, no need to get your hands wet, no need to buy other controllers, easy to install, easy to control. WIDELY USED: Suitable for fighting fish tanks, mini tanks, turtle tanks, horned frogs tanks, pet drinking water fountain and more. Specification: For Tank Capacity: 3L/4L Size Chart: Cable Length: 128cm/50.39inch Heater: 5.2cmx2cm/2.05inchx0.79inch Package Includes: 1 Aquarium Heater Note: Please allow slightly errors due to manual measurement and different monitors.