A CO2 Generator Recipe with Yeast, Sugar, and Agar – Slow-Release

This guide assumes that you have the hardware for a DIY setup of a yeast CO2 generator for your planted aquarium. This is a recipe to make a slow-release, long-lasting solution.

Create the Sugar Base

  • 1L water
  • 10 to 20g agar
  • 2 cups sugar
  • 2L bottle
  1. Bring water to a boil.
  2. Mix the agar and sugar together.
  3. Mix the agar and sugar into the boiling water. Boil for 1 minute.
  4. Let cool slightly (but still warm) and fill the bottle.
  5. Allow the bottle to cool and the solution to solidify.

Making the Yeast Topper

  • 1/4tsp yeast
  • 1/2tsp sugar
  • 100ml warm water
  1. Mix yeast and sugar into the warm water.
  2. Add the topper solution to the sugar base bottle.

Refreshing the Bottle

When CO2 production slows down, pour out the liquid in the bottle and replace it with fresh warm water.

If it has been a long time and all CO2 production has already stopped, then you will need to add more yeast (make the yeast topper recipe again) and add it to the bottle. If the alcohol concentration is too high, all of the yeast in the bottle will die off and will not reproduce by simply replacing the liquid with more water.


Make sure the water used in the topper is not too hot, or the yeast cultures will die and you will have to make a new topper.

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