For a low-tech planted tank of 30 gallons or less, a DIY yeast CO2 reactor can be a simple, cost-effective way to supplement CO2 without the investment or headache of a high-tech setup. It’s therefore very popular for smaller planted tanks, especially for aquarists who are just getting into the planted tank hobby.
These systems are inexpensive to build and relatively easy to maintain, although the yeast culture mixture needs to be refreshed periodically. For tanks 10 gallons and larger the risk of overdose is minimal, but for nano tanks, we’d advise using a smaller bottle and trying the setup out before adding fish, as an overdose is technically possible, and it’s difficult to monitor or control the CO2 output from this setup.
Before beginning, gather the following materials:
Once you have acquired the necessary materials, you’re ready to build your reactor:
There are several means of diffusing CO2 into your tank from your DIY reactor, some of which are much more efficient than others:
A DIY yeast CO2 reactor produces CO2 as a metabolic byproduct of yeast fermentation of sugar. There are a few different ratios of sugar to yeast, and you can experiment to find what works best for you, but we recommend the following to maintain an active, steady state of CO2 production:
Adding more yeast will result in higher CO2 production, but the sugar will also be consumed more rapidly, such that the mixture must be replaced more often. This could also lead to a CO2 overdose, especially for smaller tanks. Lukewarm water is recommended to help encourage yeast growth, but make sure that the water is not hot, as this will kill the yeast!
This is a relatively simple system to make and maintain, but there are a few pointers and things to avoid: