Did you know that if you add one tablespoon of coffee to your co2 do it yourself kit, that your output will be more vigorous and last one third to twice as long?
Interesting concept... except for one thing. If you have a little bit of coffee (less then 1/2 cup) from your coffee pot and mixed tap water into it I've always noticed several houseplants having more vigorous growth for me when watered with it..... (Do NOT add coffee to your fish tank!!!) The problem is though.... this is from making your water slightly acidic which many terrestrial plants prefer acidic soil. The problem comes in with the DIY CO2... the results of the sugar/yeast reaction makes acidic water to begin with. When you end up with water that is too acidic the reaction stops because it kills the yeast. By putting coffee in the water first it makes it closer to that point then without it. Baking Soda on the other hand would make the water more of a base instead of the acidic and end up slowing the reaction down and extending the time it can run.