Cheapo Yeast CO2 for healthy aquarium plants.

Created 01APR95 Last updated 12Oct95

Bruce Hallman

The three most commonly lacking elements to achieve healthy aquarium plants are:

If you have had trouble growing aquarium plants in the past, and can fix these three items, you will be astonished at the luxurious plant growth which will result.

The light is available economically, if you shop at a large discount hardware store. Typically you need four full length daylight full spectrum fluorescent bulbs.

The well stocked fish stores sell aquarium plant fertilizers, look for one with chelated iron.

Carbon dioxide used to be only available through the use of a steel compressed tank and regulator set up. This still works the best, but start up costs exceed one hundred dollars, even for the do it yourself method. Full featured setups can cost much more. George Booth has posted his summary of a "Do it yourself" compressed gas CO2 setup.

Yeast method, CO2 production.

In about 1993, somebody (I would like to know who) had the idea that if you were to ferment bread or beer, that the yeast could be used as a cheap source of CO2. Different recipes have been tried, and most work pretty good. Most people use an empty plastic two liter soda bottle. You drill, or melt with a hot nail, a hole in the cap to accept an air line. The most common problem that I have heard of is that the CO2 gas escapes from this hole in the cap. A sure fire method of sealing the cap, (I can say, because it is what I have used) is to seal a short piece of rigid tube in the hole with the brand name glue Goop. The Consumers Union Magazine rated glues a few years back, and found that Goop was the only glue to reliably stick to polyethylene used in the bottle caps, etc.. Other people have also reported success using aquarium silicon and also with the use of a fitting sold for drip irrigation. In any case the seal must be air tight.

Also, it is highly recommended that you install a one way check valve in the line as cheap insurance against the potential risk of an accidental siphon. This is good practice for all air lines into the tank.

The recipe for the yeast mixture which I and others have used successfully is to fill the bottle half full of cold tap water. Add about two cups of white sugar and shake until most of it is dissolved. Then add 1/2 teaspoon of granular baking yeast. I bake bread too, so I bought a 8 ounce bag at Costco for about $5. It will last me forever, and I store it in a airtight plastic bin in the freezer. This yeast mixture does not activate for about a day, so I usually mix it on Saturday, and hook it up to the tank on Sunday. I switch this mixture whether it needs it or not every other weekend, during my water change routine. If you use too little sugar, it may not last two weeks. (I bet as little as 1 cup would do.)

Don't use too much yeast, as I did once, as this leads to foaming, which will creep up the air line and go into the tank. The goal is to have a bubble every few seconds or so. I think that just allowing the bubble up in the tank is probably enough. Most people go to some effort to extend the "contact time" of the bubble with the water. In one of my tanks, I have the air line stuck in the venturi hole in the power head. In another I have a glass jar on it's side which contains the CO2 bubbles. Somebody wrote that this bubble in the glass jar method should be periodically purged, as the stray nitrogen gas will fill up the jar over time, though I think that the CO2 concentration would always be adequate. Some people use fancier "beer yeast", which costs more, and the cheaper bread yeast works fine by all accounts. All in all, I think there is a lot of tolerance with this method and you should feel free to experiment.

One thing to worry about is that if your water is very soft, with a carbonate hardness of less than say dKH of 2, that added CO2 can run a risk of instability pH. You should know your dKH if you plan to use CO2. Also, you should be pretty regular in the changing of the CO2 mixture, as if you stop and start, your pH can fluctuate, which causes stress to fish. (That is why so people will start the yeast mixture in advance, so they don't have a gap in the gas supply. Lastly, CO2 is easily gassed off of the water. Though, I wouldn't not use CO2 if I wanted to also use an air stone, power head etc.. The ideal planted tank with CO2 does not use filtration which causes a lot of water movement that drives off the CO2 gas.


Please send me email! My email address is:

To Bruce Hallman's aquarium plant home page.