I use light brown sugar with champagne yeast. The recipe I use is: 2/3 cup of brown sugar per 16oz of water, half a teaspoon of champagne yeast, and a little bit of baking soda. The mixture lasts about 5-6 weeks for me, depending on the temperature and the amount of yeast I initially add. I use a cheap, ceramic diffuser but there are probably better options for diffusing the CO2.
RAOK Club #77|The Fraternity of Dirt #112