Love this thread, this section, this site!!! This site and all involved have made my fish-keeping experience more pleasureful than I ever thought and super intriguing. I have read all post on this thread and found that DIY CO2 doesn't look that hard to do. I set up two 2L bottles for my 29g, I also have a 5g...erm....bottle for my 55g. Not really a bottle @ 5g but hopefully I can produce enough CO2 with that, vs using 4-6 2L to get a desirable amount of CO2. I just finished putting everything together, ran the tube into the filter, have a check valve between tank and T that connects the two bottles. Simple set-up, cheap start-up/keep-up, gotta love the DIY!!!!!