Red Sea CO2 Solenoid valve. Too much CO2 can reduce the pH in an aquarium to levels that are stressful for fish. For the safe use of CO2 it is highly recommended to automate the CO2 system with either a simple time switch or by a pH controller. The in-line solenoid valve connects the CO2 system with either of these devices. Includes tubing and a standard 1/8-inch compression fittings. Uses 2-watts.