I had the same question and sent a query into GLS, their customer service replied almost immediately re the system I had chosen. This was his reply (I have a 55g)
"Very popular size. I would also not advise on using a pH controller. We normally would see pH controller on big tanks 150g+ in size. With a 55g tank a simple timer for automation will work wonderfully. The Primo kit would be much better suited, along with either an inline diffuser or 70mm Atomic diffuser.
The inline are very popular due to them being hidden in the cabinet. You would need a canister filter to work it and you will need to know the tubing size of said filter.
Let me know if you have any questions. I have been building every co2 system at GLA for 10 years. Each one is custom built by hand one at a time. "
Also, after looking at your link to the Atomic, I noticed, it has a check valve listed in the included product list...So you just need a bubble counter a dual timer is also included it says
Atomic CO2 System Includes:
Atomic CO2 Regulator V3
Dual outlet timer
Choice of 5, 10 or 15 LB CO2 cylinder
Free CO2 resistant tubing
Taking life one day at a time
Last edited by Mahlady; 01-30-2013 at 02:28 AM.
Reason: corrected list