Thank you for the suggestions. With availability of parts, and no spare controllable sockets left, I've managed to wire up a 2-wire valve to an L-port.

It is open when unpowered, thereby rising pH as it draws air from the co2 scrubber, and shuts when over the pH target by a set margin.

This sends 9v (manually set in GCC) to the valve which is enough to close it and the pH should fall.

Installed last night so I'll see how it goes!

One question, what is the exact size of connector needed for the port? I am using a RJ12 6P6C but it's very loose

Thanks

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