Easy assembly: Attaching to the CO2 cylinder requires no tools. The extremely precise needle valve ensures accuracy and reliability in CO2 dosing. Strict quality control guarantees top-notch quality. A safety valve is in place to prevent accidents due to overpressure. Two gauges are provided: one displays the internal pressure (amount of CO2), and the other shows the pressure released to the aquarium. Solenoid - For those not wishing to supply CO2 continuously, the solenoid is a valuable addition. This power-driven electromagnetic valve stops CO2 flow when turned off. Optionally, it can be used to halt CO2 supply at night if desired.