Just to double check and avoid any possible confusion, you do mean a CO2 reactor and not CO2 inline diffuser? (I'm quite sure you do!)
I found when using a CO2 reactor that it completely knocked the flow from my filter. My filter(s) were Fluval G6s', they had an actual flow rate of 1000 LPH and pump power of 2460LPH, what was nice about this filter was the on screen display that showed several things including amount of flow being passed through and it was nearly halving it, I removed the reactor after a while and flow would never return to full, despite replacing the impeller etc.
Just some food for thought.
Did you try the 1 filter alone before you tried including the reactor?
If you were to assume the 10x tank turnover 'rule' then you would be looking for 3600 LPH; I'm not saying I agree with this rule and you are already making up some/all of this shortfall with your "flow pump".
Are you trying to get rid of the flow pump and just rely on spraybar(s) powered by the external filters alone?
In my personal opinion I think if you can do away with things in the aquarium then all the better
Having one spraybar powered by 2 pumps (the same) is possible, as is making your own spraybar with relative ease using some simple DIY skills, this also gives you the chance to adjust hole sizes/spacings as you wish.
I made a spraybar for my 900 which I did run using 2 identical pumps, the picture will hopefully show you how I added 2 filters to the one continual spraybar to give the most equal distribution of flow although at this point I was running it using only 1 filter as I didn't need the power. Happy to answer any questions.
Aquamedic inline CO2 reactor
CO2art inline diffuser