This is one of those cases where a picture of the configuration would be very useful. I believe the reactor should somehow be placed in a vertical position for best results. Otherwise you'll likely have a much greater volume of Co2 build up dead heading for the entire length of the cylinder, and may encounter belching at higher flow rates.

The simplest way to achieve a controlled misting application with a canister filter arrangement would be to use a double T manifold for two needle valves and bubble counters eBay: 2 way Brass Co2 splitter, for solenoid gauge regulator (item 250018659638 end time Jul-10-07 18:02:50 PDT) and placing an inline mister such as the Cal-Aqua L abs inline unit. CAL AQUA LABS - CO2 Glassware This would allow you to independently adjust the rates for both dissolved Co2, and ambient mist.

I don't believe there is any one perfect distribution for Co2 in a closed system. Whether it be Dissolved or Misted Co2 or a Venturi Reactor. For the most part Dissolved Co2 is the most economically efficient application for the hobbiest, but Plants definitely do enjoy some percentage of misting and make more efficient use of Ambient/Gaseous Co2. HTH Prof M