You will need CO2, unless you want to have an algae farm.
DIY could work, but it is more about maintaining a stable, sufficient CO2 level. DIY CO2 usually is not very stable, so this is a disadvantage. 29 gallon is also bordering on the size where DIY CO2 begins to become a major hassle.
In terms of pressurized CO2, you can either purchase a pre-built regulator assembly, or gather the parts yourself and assemble it. The latter is a more "fun" experience, if you like DIY work, and can potentially be cheaper, especially if you are patient and take advantage of sales on eBay and/or the Swap and Shop section of these forums.