Too good to be true?

save yourself some money, get 2 2L bottles (if its the 2.5g, use 1), some sugar, some silicon tubing, a T connector, a smaller pop bottle and some yeast (bakers yeast works well)

drill a hole smaller than the tubing in the caps for the 2 2L bottles. force the tubing through these holes, connect these two to the T connector. Drill two holes into the lid for the small bottle, force enough tubing to about 1/2 down, this tube will connect to the T as well. Force another section of tubing only about 1" down, this goes to your tank. Fill this bottle with water to about the half-way mark.

with the 2 2L bottles, fill with water up to the top of the label. pour 1 1/2 cups of sugar, mix well until dissolved, add 1/4 teaspoon of yeast.

Diffusion method varies, I have mine go straight into my canister filter. A small airstone that requires a little pressure to force bubbles would work. Placing it under a decoration works well too.

I like the hagen system a lot. I use home made cannisters on one of my tanks, but the hagen on 2 others.. .and I use the hagen bubble ladder on all of them. for the beginner, I think the hagen system is the way to go. not only is it easy to get up and running, but the ladder gives you a visual indication of whether it's making co2. you can switch to normal yeast (non-hagen) when the packets it comes with run out.

here are some pics.

http://www.qsl.net/w2wdx/aquaria/diyco2.html#4

It doesn't use 2, but for anything above a 10g, I would use 2. I have 2 reactors on my 20, plants pearl like crazy. I'd replace the solution every 7-10 days. Hagen system boasts a month before you have to replace, but by that time very very little CO2 is being generated. and no, it does not matter which port you connect to on the T connector. As long as one leads to the small pop bottle.

I agree with mellow the hagen system is the way to go for the beginners I started with Diy and went to the hagen because of the ladder for small tanks its great I still use it on a 10g .
check around I have seen it much cheaper

here is the recipe for when you run out of the packets that come with it

For the Hagen Nutrafin Canister:

Sugar to the bottom inside line,
Water to the top inside line,
1/8-1/4 teaspoon yeast
1/4-1 teaspoon baking soda

credit goes to John N of APC

I bought some for my smaller tanks, and love them. Like Draal5, I got them mostly because of the ladder. My larger tanks that have canister filters use simple DIY jobs, running directly into the canister syphon line.

note, you don't need to buy their refil packets, a sugar/water/bakers yeast or brewers yeast works just as well, if not better, and is a lot cheaper in the long run.

Place the bottle wherever you want to hide it, and let it run as long as it's producing bubbles at a decent rate I have a tendency to forget to refil the thing, and eventually when I'm looking at a tank, I'll notice that it's not producing any CO2 , so I'll refill it. My larger tanks are easier because I go with dual 2L bottles, and alternate one each week, whether they need it or not, and only change 50% of the liquid with new sugar water, and the yeast will just keep going. Cheaper like that.

edit: forgot about your question about holding the bottle. No, you don't have to hold it, unless you have a couple weeks of spare time and feel like it... DIY CO2 systems are basically set it and forget it, until it needs a refill.

Petsmart carrys this item now too, if you have one locally, so you could save time and shipping, check the petsmart website for pricing, and the store will match their (petsmart's) online price...