one or two bubbles is not that much mist, I don't know where you see the video, it is misleading, because you may see the part that the bubble rate has been dialed down but the diffuser still pushing out a lot of mist due to prior large bubble rate.
1. cut a short section of the air hose, and burn one end, pinch the soft plastic to make a seal, plug the open end into the quick connector, and it is a "no pass" for the co2.
2. charge the regulator with co2, the HP gauge is 800 psi, the LP gauge is whatever the output psi that you desire(30-50psi).
3. close the co2 tank and leave the solenoid power on for 6 hours.
4. check the HP and LP gauge, if the HP gauge lower, there is a leak, if not, no leak.
I am pretty confident on your system though, It was checked.