Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
The production rate is controlled by both temperature and the amount of yeast you add. Add twice as much yeast, it produces twice as fast.
The production time is controlled by both rate and the amount of sugar you add. Production starts to slow when sugar starts to run out, or alcohol (the byproduct) rises to the level where it's toxic to yeast. Whichever comes first. If it starts slowing down and the solution tastes more than slightly sweet, you've added too much sugar. Reduce sugar. Or use more water (and probably a bigger bottle), which will keep the alcohol more diluted.
Simply really. Mix up one batch. Use a drop checker to determine what CO2 level it produces in your aquarium, and for how long. Then use the rules above to modify your recipe as needed.
My base recipe:
1.5 cups sugar
1 tsp. Fleishmann's Active Dry Yeast
2L bottle filled to the bottom of the neck with water
Which I know from experience produces 30ppm in my 10G for about two weeks. Your results may differ, and that's where the drop checker comes in.
But if I want to add 30ppm CO2 to a 5G, I know I'll be fairly close if I cut the yeast in half.
And for a 20G, I double the yeast. Which doubles production rate, and cuts production time to one week; so if I want two weeks as well, I also double the sugar and water (bottle size).