This is actually the third reactor I have built. The first was a verges style. I switched to a RG style for space / routing purposes. The one I am using now is made of 4" PVC. I am downsizing because I am barely getting any flow from the output of the filter. I am running the filter (API XL - same as old xp4) output through the reactor, then through my inline heater. I have an fx5 on the other end of the tank, but I don't get enough flow on this end, plus I want to make sure the co2 gets distributed throughout the while tank.