Aquasport, there is no controller. I'm measuring the pH of the effluent rather than hooking the solenoid up to a controller, per the instructions here (see "Running Continuously", bullet #11). Please let the thread get back to my issue, which is, why does my CO2 feed stop bubbling? I dial in a certain bubble rate per minute using the needle valve, and that rate drops to zero over time. Erik suggested that I use a rubber band to keep the needle valve knob from moving. I'm hoping others will chime in with some more thoughts.