Solenoid cycles on CO2 to reactor: how often is too often?

[Delphinus]

Got a link for a 1/4" valve? I'm currently using this one (which seems to have good customer feedback, but is 1/8" not 1/4")

I have the thing currently barely open. If I close it any further I don't get consistent gas flow into the reactor. I've tried lowering the regulator output pressure so that I could open the valve more, but again I get weird effects when I do that. Ie., either the bubble rate stops altogether, or the reactor effluent stops .. stuff like that.

I'm all for using less CO2 though so if the answer involves moving to a different needle valve I would consider that.