While I understand that I could buy a commercial unit with the tank for around $150.00, I'm living in an area where I cannot get the tank filled. More specifically, I live in a small rural town and it is 50 miles from even the nearest Wal-Mart. There is a place that fills paintball cylinders, but they will not fill larger tanks. SO, after playing with DIY CO2 for a while, I too wanted to upgrade.
I could have bought the Red Sea unit, but what fun would that be!
After looking at the options, I decided to go with a DIY project. The problem that people seem to have when embarking on this DIY project, (the same one I initially had), is that the regulator doesn't hook up to the paintball tank. Well since I did some research, I figured I'd share my findings.....
First off, all these regulators come with CGA threaded fittings. All that means is that the 'Compressed Gas Association' came up with different threads to connect different gas tanks up to the proper regulator. It's all about safety. You wouldn't want someone accidentally hooking up Acetylene (a highly flammable gas), in an application that required inert gas, such as CO2. That being said, high pressure regulators that we need to use in a pressurized CO2 application are basically built the same...whether it's intended for Oxygen, Acetylene, CO2, etc. What changes on these regulators is the threaded end that connects to the tank.
My idea is simple. Probably not the first to do it, but still easy enough that it bears repeating. Remove the CGA threaded fitting! Another thing that these regulators have in common is that they have NPT (National Pipe Thread) threads that screw into the regulator body. Note - I haven't checked every regulator on the market to ensure that
every regulator is equipped with NPT threads, but I did look quite a few of them up and it is common enough that I didn't even see one advertised with anything other than NPT. What this means is that your local hardware store has the required parts to finish the job.
Here's a picture of the setup:
Here's a close-up of the required fittings:
The 1/4" Nipple threads directly into the regulator body once the CGA fitting is removed. I didn't take any pictures of the CGA fitting, but just about any picture on the internet will show you what it looked like before. Next, thread the reducer onto the 1/4" nipple. The reducer is required because the Paintball remote came with a 'Quick Disconnect', (the kind on an air compressor only smaller), and the thread is 1/8" NPT. The reducer mates these two sizes together. Finally, thread the quick disconnect from the Paintball remote into the reducer. Make sure everything is tight! Use pipe joint compound if you have it on all the threads. I had some PTFE lying around and used it instead...I'll have to see how that works over time. The compound/PTFE keeps the CO2 from leaking out of the threads.
The medical oxygen regulator that I got is nice because it is already built for low PSI applications on the output side....you wouldn't want 200 PSI blowing up someones nose!

A needle valve inline is recommended however, because the pressure we use on our tanks is
really low and a little finicky to get dialed in on the regulator.
If you look it up on the internet, you'll also find that the burst pressure ratings of 1/4" galvanized pipe is far from the tank pressure of even a full sized CO2 tank. Somewhere near 3000 PSI for 1". I couldn't find a value for the smaller pipe but 1/4" pipe will have an even higher burst pressure rating than that, and much higher than the tank pressure. So, it is safe!
Breakdown on the cost:
$15.00 for the oxygen regulator on Ebay.
$23.00 for the Painball Remote on Ebay.
$0.96 for the 1/4" to 1/8" reducer
$1.17 for the 1/4" nipple
$24.95 for the Paintball Cylinder
$2.50 to fill it.
Total: $67.58
That's it....just add your favorite reactor/diffusor, needle valve, and check valve and it's ready to go! It's been running now for two weeks without a problem. I figured I'd give it a bit of a test before I posted.