When I was first getting into aquariums, I got sold at a local pet store on a wet/dry state of the art sump system I had to have. Don't know what I was thinking, but I guess I trusted the guy to guide me in the right direction. Needless to say, when I got into planted tanks with CO2 injection, I use 2 rena canisters and the wet/dry system collects dust. But recently I've been contemplating an idea I've had for awhile.
First of all, I have a 75 gallon tank with CO2 and 260W of light. Not that any of that is real important, because the idea I had was for the sump. I was thinking of sealing off the sump and replacing the overflow box, tubing, etc. with PVC pipes with a number of valves for water changes (my tank is somewhere I can hook it up to the plumbing). This way I minimize contact time with the air that occurs from the box in the tank and the overflow on the back of the tank. Once the sump is sealed, then I could inject the wet/dry area with the bio-balls with the CO2, instead of in an inline reactor. Making the pump and filter pads accessible and having the sump airtight will be a problem. Pressure regulation on the CO2 line into the sump will be a problem. Probably a bunch more issues I haven't thought of yet, but I'm looking for some input.