I use 1/2tsp of ordinary yeast and a pinch (less than 1/8tsp) of baking soda. My water here is GH/KH=1 out of the tap so I add the baking soda. You might not need any if you have harder water.
My CO2 lasts about 10-12 days. I can't explain the variability. No matter anyway since I change the bottle each week when I trim and change water.
good luck
jtm
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