M-Ventil Aqualine Buschke German Solenoid Valve. The M-Ventil solenoid valve, in conjunction with a timer, can be used to turn off and the supply of CO2. If connected to a pH controller, the CO2 can be more accurately controlled. CO2 is then supplied to the aquarium on demand. The M-Ventil is chrome-plated, and has a low power requirement and low operating temperatures.