I posted my DIY details at the other section but would like to share my recent project with other people.
First off, my DIY CO2 system is very over-spec.; means I used all connections, except for the regulator, with the products we make at our company. (www.generant.com
I got a regulator from beveragefactory.com and connected 5/16" PVC tube to the reducer fittings. Initially the regulator came with 5/16ID x 9/16OD tube but we do not carry any products with 9/16OD, so I bought 5/16ID x 1/2OD PVC tube $.36/ft. The regulator was $38. Then I reduced the size of connection from 1/2OD to 1/4OD to accomodate 3/16OD aquarium use silicon tube. I used our needle valve and connected to the soleniod ($30). After the needle valve I used industrial grade brass check valve, then the silicon tube goes to diffuser/bubble counter (from Hagans fermentation kit, $9.90). I got 5LB aluminum pressurized CO2 cylinder from the local fire extinguisher company, who comes to our facility for fire drill once a year. The cylinder was $48 and refill will be $5.00 thereafter. The overall cost was a little over $100 and I am very happy with it. I am still waiting for the bubble counter to be delivered next week so I should be able to take a photo of the entire system. Fittings, check valves, reducers, needle valves are all free. My DIY setup will look a lot bulker than others because all the fittings and valve that I use are not for aquarium use; they are for very high pressure industrial gas, cryogenic industries.
It took me so long to think about and initiate my project but I am so glad I did.