Nice solenoid. Yea, I think what your saying is right, about the excess CO2 being in the regulator, and not in the line. I watched my co2 after the solenoid switched off, and my diffuser stopped bubbling within a minute. I was so excited about shutting my co2 off a few hours before lights out too lol.
looking forward to pics of your white clouds. I went with 5 CPDs.