I don't see any purpose to the secondary loop. You won't want to use that to adjust the amount of CO2 in the water - adjusting the bubble rate works much better for that. And, the rated flow of the pump pushing water through this is with no restriction on the outlet. The reactor is a restriction, so the flow rate will be less than the rated flow, possibly down to 100 gph. It is just an unnecessary complication, and source of possible problems.