This looks interesting and I assume it works just as well or better than commercial models. Did it cost less to build than to buy the commercial product?

Just noticed your question, but to answer your question- Yes, far less money. The problem with most of the commercial ones is they don't have everything necessary to efficiently saturate the water column with the CO2. The Hagen and Red Sea both have fine generators. The Red Sea got the idea to add a small pump rather then a difuser which improves saturation. I did find one unit made in the UK ( I think) that had all the right parts. I have never seen one like that in the US. The bubble counter/gas seperator is important because it "refines" the CO2 before going into the tank. Anyone that has used Hagens will find they often get clogged with white "fluff", a by-product of the fermentation mixture. It is not harmful to fish but is a PITA to clean and reduces effectiveness of the CO2. The reactor ( the one pictured is an out-of-the-tank kind)is the same as the Aqua-Medic 1000 that sells for about $60, except a smaller version. I also have made, and still use in-tank reactors. You may have seen them on other sites and DIY articles. The kind using a gravel vacuum tube, with a low flow pump. I have made these for a few people and they really like them. I actually sold one on ebay the other day, I wanted to see if it would sell. I will be putting more on ebay and other fish boards that have a forum or sales. I made enough with these and the sale of some plants to get a compressed CO2 system with a 4-way manifold and a pH controler for one tank. This is a nice way to start out with CO2 because its inexpensive compared to compressed CO2. And if you decide to "upgrade" to compressed the bubble counter and reactor are suitable for compressed. With this system I was able to maintain my pH in a 29G tank with 4 watts per gallon at 6.8-7.0 before the lights come on and 7.4 beore they turn off. I have improved this since I first built one last year. I wanted to start another strong light tank but didn't want to pay or a kit that I would only use part of. The link below is an article step-by-step for my generator, the first one I built. Mine is the white PVC one or "Squidheads". It has evolved into an easier to use, build and less expensive model.

Here is a link that might be useful: CO2 DIY Article

Thanks for the info!