building a Co2 reactor for my fx5, should i go with 2 or 3" OD tube for the main portion of the reactor? main filter lines are being switched over to 1" pvc all the way. reactor will be about 18" long. anybody have any input on this? I had planned to do it with the 3" but im a little worried that will slow the flow down too much so im thinking the 2" would be better for keeping flow rates up.