I've tried both Cerges and Rex Grigg style reactors on a 55g tank. I've found the Cerges works better, is more efficient, and over all much less work building. If not a little more costly because you're buying a commercial product.
For my 125g w/ 40g sump I naturally chose to go with a Cerges stlye reactor using: http://www.lowes.com/pd_89378-59019-...t=water+filter
as the base.
Easily enough, water goes in, water goes out. I tapped the PCV going into this for my co2 line, and currently have some sponge filter media inside it, along with clear PVC tube inside.
Currently, I get a TON of microbubbles. I blame the flow rate of my pump, which i believe is a rated 1800gph fluval submersible. But i also wonder if the cerges reactor is efficient enough for a tank of this size with a pump rated at that?
After HOURS of the co2 blasting into the tank, my drop checker remains blue. Which leads me to believe that all those micro bubbles mean that the co2 isnt dissolving, but just being shoved into the tank.
My next step, i think, is going to be shoving pillow stuffing into the reactor as well and hope that is enough to break the co2 into finer bubbles before exiting the tank.