Since you have both, As Tom W said, use both.
Simply raising the overflow box part to about 2-3" below the tank level will help.
Also, plug any holes in the tower for the wet dry section that might exchange air with the dry part of the chamber.
Feed CO2 outflow from the reactor directly into the return pump.
also, make a DIY CO2 reactor and add a venturi loop to this. This is the best method for CO2 on large tanks, well, there's another way if you want to use a disc plate and pump the gas directly into the tank. Both methods work well.
I'd get a pump that does about 1000 gph at 4ft head for the return.
you will get the benfits of the surface skimming as well as a constant level inside the tank, and a place to put heaters, do water changes, dosing pumps, CO2 stuff etc if you use a sump.
I hate the water level moving due to evaporation on large tanks as refilling them stinks. You can expect 10 gal a week on this tank, not sure if you wanna do that or look at that every week.
I'd load the sump and cansiters up with 20-30 open cell foam and use plain bioballs in the dry part of the tower. Bacteria will grow well as the O2 is still high in the water, and give off CO2 as they respire, so as long as the system is sealed inside the dry part, no exchange will take place except what the bacteria convert.
Many people will tell you all sort of stuff on this issue, don't believe it.
We tested this in the 1990's and 3 folks all found indepentdly the same things about this.
Tom Barr www.BarrReport.com