Ah. I see. It was sort of hard to make out from the pictures. So it looks like there's two tubes near the powerhead? One is its own tube to grab oxygen on the output and you run another tube for co2 down to the bottom of the powerhead's intake in attempt for it to suck it into itself and break up the co2 bubbles to smaller ones?
While that method may work, it may not work well enough for your needs as the bubbles are possibly not being chopped up fine enough to make a big difference. As such, the bubbles when it comes out of the powerhead, just floats up to the surface and .. well, vanish (wasted) instead of fully dissolving into your tank water. Is this what you're observing?
The reactor that you have may help if you feed the powerhead to its intake, feed the co2 to the little tube connector up top and let it all swirl around in the reactor as it dissolves the co2 into the water. The theory of the reactor is that it keeps your co2 trapped until its all (or almost all) dissolved into the water before it lets it out. And you'll probably need some sort of elbow on top of the reactor for the new water outflow lest it shoots straight up from your tank! Otherwise, most people run reactors inline with their canister filters as there are already expected inflow and outflow tubes.
Here's a nice guide on how co2 reactors work and it's a very good site overall for all things planted tank!
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