[woody123]

I Have a 55 gallon and a 75 gallon in my office, I run two filters on each one. I have them setup just the way you described. I really like the setup as I get good surface agitation and a lot of filtration with two filters. I use an Eheim pro 4 250 on most all my tanks. The 55 Gallon has one reactor and one CO2 setup I get a 1.0 PH drop and everything is growing well so I assume I have good distribution of CO2 for my purposes. The 75 Gallon has two reactors and two CO2 setups, this is really overkill for the size of tank the only reason I did it was because I had the equipment, and I don't have to change the CO2 tanks out as often. A 120P is a great tank good luck with your build.

The first picture is the 55-gallon (this tank is only about 3 months old, however I have used this same setup on many tanks) second picture is the 75-gallon setup.

 

[woody123]

I just used the basic inlet and outlet pipes the filter came with. I like the lily pipes; however, my tank is kind of built into my desk area so it would be hard to get a glass lily pipe off to clean it periodically. Yes, one CO2 setup for a 75 gallon is plenty, I just did two because I could go longer without having to replace the tank. If I removed the second one I would just increase the CO2 flow on the first one to make up the difference.