Olga, Addition of baking soda into DIY CO2 mixture will last for longer because: (1) In anaerobic condition, the solution become acidic gradually, it will\ slowly limit the growth of yeast. Baking soda can neutralize the acidity to a certain degree. (2) During baking soda and acid's neutralization, you will have some CO2 produced as by product. And hence, more co2 bubble into your tank. rickie