I decided to start a new thread for this so it doesn't get cluttered up with the other one. First of all let me start with the plan so you can see the development of it. This is the line-drawing of the reactor design. It has a half metre length of clear PVC, Grey PVC socket and bend at either end (they don't do the clear fittings in metric measurements!), 2 threaded reducers (to bring the 1.5" threaded sockets to 1/2" threaded) and 16mm or 12mm hosetails that fit into the 1/2" reducers. The CO2 is injected inline ahead of the reactor (using a reducing tee) so the CO2 and water are already mxing up before they even enter the reactor. The water/CO2 mix enters at the top of the reactor and then rushes and swirls around in the large reacting chamber. By the time the water reaches the bottom of the reactor there should be no bubbles left at all in the water so bubble-free, CO2 enriched water will be reutrned to the aquarium.