As an innovative solenoid valve for semi-automatic control by means of a timer switch or for fully automatic control by means of a pH value regulation, the solenoid valve pro can also be connected directly to CO2 Armatur Pro. If controlled by a timer switch, the normally closed Solenoid Valve Pro interrupts the CO2 supply and can thus save up to 50 % of the CO2 consumption. Since plants do not consume any CO2 at night, the solenoid valve should be synchronised with the light control of the aquarium in this context. In combination with a pH value regulation the CO2 supply is optimises because the volume of CO2 is dosed exactly to the amount that is consumed. Thanks to the electronic diode circuit, operation of the CO2 Solenoid Valve Pro is extremely quiet, energy-efficient and with very little heat generation.