I'll have to study this reactor a bit more when I get time, I'm not familiar with it. But with an Eheim 2215 and being used on a 150, I don't see how it could hope to ever get the CO2 levels up to where you want them.
BTW, I'm not quite sure why 2 pumps in one line would make much difference, water in has to equal water out, and that 2215 canister full of media and gunk is going to slow things down quite a lot.
6' Planted Tank (72" x 18" x 20") - 4 x 30W T8 Tri-Phosphors - 2 x Eheim 2217 'Classic' canisters
Flourite substrate - Ocean Runner OR-2500 + AM1000 - Tunze Turbelle Nanostream 6045
6.8kg Catalina CO2 - Red Sea Pro regulator - Swagelok B-SS4-A metering valve - Vecton 600 UV