i would recomend if your not looking to bust your wallet for a decent co2 system to use the diy idea.
and here it is. compliments to: www.boroniaaquarium.com.au
Here's how to build your very own carbon dioxide cylinder -
Get a 2L soft drink bottle, drill a little hole in the cap and attach an airline tube to the opeining with silicone.
Attach an airstone to the free end and this is to be placed in the tank.
To the bottle, add some brewers yeast, some water and sugar. You may have tried this before and noticed that this reaction is a little difficult to control.
So, the secret is to add a couple of teabags in your mix.
Another tip is to ensure as little resistance to the gas outflow as possible, use a shorter length of tube.
i hope this has helped you a bit.