Definitely use the CO2. Looks like all you should need is a brass check valve and a diffusion method of some sort wehter it be by Diffuser, reactor, mazzaei injector, needle wheel pump. Lots of info on each in the Equipment forum.
I would say use the canister. Actually an Eheim 2217 would be better maybe you cna sell the FX5 and get an Eheim.
How do you like the 33g Long. I was so tempted to get one or even the 40 long before going with my Nano ADA setup. I still dream about setting up one maybe someday. I would prefer it to have the 75 depth of 18" though.
Enough rambling from me though.
Fluval Spec III Shelf!
"C'mon, they're just plants, man, no big deal -- try some"