This is what I think needs to be done. Release the pressure in the system by shutting off the valve on the tank and letting the trapped co2 in the valve out. what might be happening is you are adjusting the pressure on the other gauge but the pressure has to be released inorder to register the change on the gauge. so tighten the bottle valve, remove the co2 line from the reactor, plug in the solenoid, open the needle valve, evacuate the co2. reopen the tank valve, adjust the pressure down with the knob on the regulator, close the needle valve, reconnect the hoses.