Gas exchange into CO2 bell?


Junior Poster
Nov 10, 2008
Raleigh, NC
I am creating a DIY CO2 system that uses a bell to hold a reserve of CO2 to moderate the inconsistent performance of the yeast/ sugar.

My question is: If the yeast stops producing, but gas is still present in the bell, should I assume that the gas is CO2, or would other gasses diffuse in and take their place? Will the bubble eventually disappear as CO2 enters the water (it has persisted for a week since the yeast culture died)

I know that I won't get a huge amount of CO2 by this method, but my priority is stability.

Henry Hatch

Guru Class Expert
Aug 31, 2006
Passive reactors like co2 bells are not as efficient as a powered reactor. There are a number of designs including those noted on this forrm. Generally powered reactors use a siphon tube or small plastic bottle with the bottom cut out with a power head on top and a sponge on the bottom. The power head churns the co2 bubbles until they are dissolved. The sponge prevents the bubbles from escaping before they are dissolved. There is a venturi type reactor designed by Tom which is one you might try.


Guru Class Expert
Jan 22, 2008
Vista, Ca
waehner to answer your question, no other gasses should form under the bell just co2. With the bell you are not getting much stability as the co2 diffusion is really localized around the bell unless you have some sort of power head blowing across it. i would recommend a small venturi as henry did, i used to use one that i fashioned out of a small rio powerhead and viewtainer i purchased from homedepot. As stated by Henry the plans are on the forum. For my yeast days it worked extremly well. However make sure you put backflow protection on the line. I didnt do this and the powerhead flooded my co2 bottle... :( , a simple one way air vale is all you need somone between the yeast and the powerhed.

Also as far as the bell moderating the amount of co2 i dont think that is true. It will diffuse as much as it can depending on the amount of water passing by. This is the beauty of the venturi reactors it in sense simulates about 1000x the water circulation around a bubble of co2 dissolving it in a matter of seconds vs days or hours. Also with yeast i simply placed the power head on a timer and at night the gas build up simply bubbled to the top with no adverse fish reactions. If not you can leave it on 24/7 and it most likely should prove no problem with the fisheys.