CO2 Yeast Generator

CO2 Yeast Generator


By: Fred Goodall

This is a variation on the standard DIY CO2 yeast generator. Instead of using a 2 liter bottle and 1 to 2 cups of sugar, I use a 3 liter bottle and only 1 cup of sugar, and only 1/2 a teaspoon of activated yeast. Useful production for a 55 gal tank is about 14 days of steady, even production. I use straight tap water, no dechlor. On day 13 or 14 I pour 1/2 of the volume into a second bottle and fill with tap water and add 1/2 or 3/4 cup sugar, and reseed the culture with less than 1/8 teaspoon activated yeast. You will have to determine the amount of yeast to add as the culture's growth is also depended on average temperature. remember you are after something on the order of a bubble a second and you do want to test for CO2 levels with a test kit and shoot for no higher than 25 mg/l or 25 ppm both measures are the same, just different terminology.

Construction is quick and easy, safe also, as long as you put the cap on the bottle and hold the bottle while drilling the hole in the cap. If you under size the hole and cut the air line at a sharp angle you will have a fit so tight you will not need to seal with silicone and play with leaks. Usually these setups come with advice to use regular air stones, they work, but I found that the disposable fiber air "diffusers" work better, providing finer bubbles and less back pressure. Looking at the diagram this little project is not complicated nor is it hard! It is as clear as it looks, the mixture of the yeast is very simple, warm water up to where the bottle just starts to narrow, sugar, mix it, add yeast, screw bottle into the cap with the air line just through the cap. At about 24 hrs later you will see some foam in the bottle and some bubbles rising from your diffuser in your tank. 

In my experience the "uneven" pH derived from these units is from the "overloading" of the sugar and the yeast.... it will give you CO2 inside of 12 hrs... but it goes like an air stone on full blast for a day or two then keeps on a steady decline. Making pH drop then start rising. With less sugar and yeast and more water to start with the CO2 generation takes longer, last longer and is much more even over 15 days.

Item list:

3 liter bottle
air line tubing
air diffuser or air stone
sharp scissors
3/16 drill bit 6mm


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