To help alleviate PH swings associated with my DIY CO2 going into the tank 24/7, I have my CO2 going through a gang valve, and I can control it going into the tank by opening and closing an unused valve. Problem is I don't always remember, and not always home. My question is, is there a solenoid that would do the same thing? What I envision is a solenoid that works like an A B swich; one input, and two outputs. When the lights are on, the CO2 is routed to the output that goes into the tank, when the lights are off, it would switch to the output that would just vent into the room. Remember, this is DIY CO2, and on a porch, I'm not trying to suffocate anyone :-)

I realize the solenoids typically used with pressurized systems wouldn't work for what I'm asking. When I look for solenoids online, there are so many types available, I don't know where to start, I thought someone here might be able to direct me to a type that would do what I want. Thanks in advance!

There's two basic ways to control DIY.

One: powerhead.
Feeding the CO2 into the DIY Venturi internal reactor (search here in "articles") amd simply plugging the powerhead into the light timer accomplished this for the cost of a powerhead............8-15$ depending.

Or you may use a solenoid, but that does not save you any gas like on a Gas tank CO2 system............you also need to make the Tee and have the solenoid "open" when you do not want the Gas to come into the tank. The gas just vents to the air instead of going into the tank.

When the solenoid closes ( normally an "off" position), the Tee is now closed and the line pressure builds up and goes into the tank and adds CO2.

This a "reverse" solenoid method.

It just bleeds the gas off until you need it.
If you try and stop the gas without any venting, the CO2 production goes way down, most folks pop their bottles or caps, or they leak etc and do not work afterwards.

Powerheads are far cheaper.
When they are off, the gas just vents into the air.
Otherwise, the powerhead grinds up the CO2 bubbles and diffuses and dissolves them.

Regards,
Tom Barr