Tank here is 4ft with the co2
going into a tunze c02 diffuser on one side and there is a ph probe on the other side. The ph probe connects to an ISTA controller/regulator on the gas bottle. The probe turns off the gas once ph drops to 6.9 or so and then re-starts when ph lifts again.
I believe most just have a co2
ceramic stone - I had this at the start. It sat under an internal filter so the bubbles got sucked into the filter to mix around more.
I bought the lot as a package deal from a lfs
. If you can find someone at the shop that does c02 injection then they can explain/help as well. It seems complicated but once up and running is little work.
Make sure you get a regulator with a fine needle valve. The ISTA doesn't have this and I find just changing the valve a fraction changes the gas flow rate a lot.