One caution: don't put yeast into a bottle of hot water. It kills the yeast. The water should be barely warm to your finger - that helps the yeast get growing.
I started a DIY 3 liter bottle on my 45 gallon tank about a week ago. It is still churning out the same bubble rate. I used 3 cups of sugar, 1 tsp of bread machine yeast, and 1 tsp of baking soda. After a few weeks I will have a better idea about just how practical this is - I do know that I get about 20+ ppm of CO2 in the 45 gallon tank, and only use a simple air stone under the canister filter inlet. I plan to make a Cerges style DIY reactor in the next couple of days and run it in the filter output line.