Did you also get the following?
Solenoid, Timer, Diffuser/reactor, Bubble counter, Co2 tubing, check valve?
You need these to run the system and it also depends on how large your tanks are on the reactor or diffuser.
Why two systems? Are your tanks far apart?
I just purchased a 5# new tank from these guys cheapest I found on the net...
http://www.beveragefactory.com/draft...anks/co2.shtml
Personally I'm going to build a reactor my tank is 135 gallon, and use an external Eheim 1253 pump I have,
Google Co2 and you will find a ton of reading..
Hope it helps.
John