22 How does the yeast method work?
Description
This article is from the Aquaria: Plants FAQ, by multiple authors.
22 How does the yeast method work?
CO2 is generated by fermentation of sugars in a bottle (just like when
brewing beer!) and then injected into the tank using the same methods
described above. The parts are very cheap and easier to set up than
the compressed tank. The main drawback is that CO2 generation rate can
be erratic, and will quit on you if you do not change the solution
(once every two weeks or so) or get the mixture right. The CO2 level
generated is lower than that of compressed gas tanks, but is still
enough to help plant growth. Initially passed off as "useless" by
much of the aquarium literature, this technique has enjoyed a certain
vogue in the last few years as a good way to try CO2 without draining
your wallet.
Here is one quick construction method: Tap the cap of a 2-liter
plastic soft drink bottle (the author uses drip-irrigation taps, which
can be obtained cheaply at local hardware stores; if you get leaks,
try sealing it with "Amazing Goop" or "Shoe Goo") so that an
airline tube can feed the gas into your tank. Half fill the bottle
with water, and add 1/2 tsp yeast and 1/2 cup (or more) sugar. The
solution will last about two weeks, after which you can throw it out
and start a new batch. Beware of water siphoning back from your
tank... put a check valve in-line with the airline tube.
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