I suggest that you find a 100-200 gph submersible pump (at that small size they aren't usually called powerheads), make a spraybar to fit the outlet pipe, with the bar being almost as long as the tank, then set that at the back and at the bottom of the tank, with the spray holes directed towards the front of the tank. Then just poke the CO2 line into the inlet grid for the pump so the bubbles get chopped up by the pump rotor and sprayed all over the tank. It adds a lot of current, and quickly fills the tank with CO2 mist. That's what I use, and I'm very pleased with it. I used transparent acrylic pipe - 5/8 OD - 1/2 ID - from Tap Plastics, where I also picked up a little 1/2" disk of acrylic and some cement to stick it in the pipe to close it. Very cheap and effective. I did have to take a small file and file off a bit of the barbs on the pump outlet pipe to make it fit easy into the tube.