FORGET IT. Its not efficient to control or maintain high levels and smells stonger than your buds will. But if you insist on this method, a pound of sugar added to warm water (fill 1/2 of your 5 gallon bucket) and 2 packets of baking yeast. The yeast eats the sugar and Co2 is the biproduct. last a couple of days and smells like stale beer 10-fold. Another science fair method is a vinegar drip over baking soda and less smelly. If your serious about healthy plants get a tank system.