We highly recommend the Geo. It's the easiest to setup, easiest to maintain, and buffers just as well as the high capacity Schuran, if not better. The unit is reverse flow, which is a little more efficent than standard top down flow, and keeps the co2 recirculated within the unit. It also comes standard with a PH probe port in the top of it if you choose to use either a monitor or controller with it, or you can just plug it up with a pvc male threaded plug if you do not want to run a monitor or controller.
If you have any questions please let us know!
Thanks,
Jeremy