Maybe i missed it, but are you injecting the co2 into the reactor? i assume this is the case, i found it much more efficient to inject the co2 into the return pump, the co2 gets chopped up before entering the reactor and the turbulence helps it dissolve quicker. Im afraid you might struggle though with the cerges, it simply doesn't have the volume needed to dissolve the amount of co2, especially once you get to 30 ppm of co2, it takes much longer for the co2 to dissolve, and you end up with a reactor just full of air, and wasting a bunch of co2. But, try chopping the co2 with the pump and see if that helps.
I would really recommend building a rex style, i think the pvc parts are about 15 bucks, definitely worth a shot! Build it as high as you can, run the co2 into the return pump so it gets chopped up, the larger volume prevents co2 from escaping and being wasted. Another little trick is use a long tube that goes from the return pump to the reactor, maybe a 6 foot tube you can coil up, this gives the co2 thats chopped up more suspension time before hitting the reactor.