Science Buddies: "Ask an Expert"

Hello,

My project concerns the effect of greenhouse gases on marine life. I am going to recreate a closed marine ecoystem using shrimp, java moss, live sand, and java fern. I plan to have three seperate ecosystems. My variable will be increased and decreased levels of CO2. One of the ecosystems will not be affected by the variable and will serve as my control. With the other one, I plan to use calcium hydroxide to decrease or eliminate the carbon levels. The one with increased carbon levels is the one I have problems with. How can I increase the amount of CO2? I was thinking of burning a paper but would that produce carbon monoxide or some other substance...? Is there a way to controllably increase the CO2 levels? Also, is there some sort of meter or chemical process that can determine the amount of CO2? I am also having trouble with the title. Any suggestions would help. Any information will help.

Thank You

Hi BleuFonce,

Sounds like a neat project.

Household methods for producing CO2 are fairly common among indoor plant enthusiasts and exotic aquarium fans, so a bit of web searching may turn up some worthwhile information.

One option is to purchase bottled CO2, but the hardware will probably be quite expensive. (Probably of order a few hundred dollars if you buy it new.)

A much easier method is to use yeast to generate CO2. A 2-litre bottle in which you've put room temperature water, sugar, and baker's yeast will generate CO2 that can be piped into your tank. You'll have to experiment to get a feel for what sort of mixture is appropriate and how long it will last.

Measuring the CO2 concentration in air is tough. But, you can get a reasonable measure of the concentration of dissolved CO2 in water by measuring both the pH and the alkalinity of the water. Aquarium stores or educational chemistry vendors can supply the materials you need to measure both. From that and the temperature, you can probably estimate the CO2 concentration in the air above the water if you want to know that as well.

Here's a nice collection of articles that includes a thorough discussion of how to measure and interpret dissolved CO2 in an aquarium and very detailed description of a home-made yeast based CO2 generator. There are also plans for a cheap home-made automatic CO2 regulator if you're willing to do a little electronics tinkering - but you may find that the timescale over which a yeast generator changes means you can get away with manually adjusting things daily instead.

http://www.thekrib.com/Plants/CO2/

One caveat - since this involved piping fresh CO2 into the tank, the system won't really be closed. (Well, if you include the CO2 generating tank and the atmosphere into which excess gas escapes are part of your system, then I guess you could call it closed.) Trying to put together a truly closed system that operates with an adjustable amount of CO2 would require a lot more chemistry and biology knowledge than I have. Then again, having more bio and chem knowledge than me is a fairly easy criterion, so someone out there may be able to help.

Finally, make absolutely sure there's a safe way for gas to escape or enter if the pressure in your tanks change. Otherwise you may end up with a big glass bomb on your hands! Drilling a small hole in the top plate of your tank and setting a lightweight object over it is an easy way to make a high-pressure relief. (A small piece of flat styrofoam with some coins or screws stuck into the top side might be a good candidate for the light object.)

The low pressure relief is a bit harder. A tube going from the outside to the inside with a balloon over the mouth of the inside part would work. A hole cut into the top of the tank and covered with a sheet of kitchen plastic wrap held in place by being weighted down with a lightweight ring is another idea. (That could also work as an over-pressure release.)

Best,
Erik

Another cheap and ready supply of CO2 is dry ice. This is CO2 in the frozen form. It is used to keep things very cold and is readily available in most areas, especially grocery stores that sell supplies to campers, as many people use dry ice in their coolers while camping or boating.

You may measure the CO2 amount by weighing a small piece of it before introducing it into your experimental environment then multiplying that weight by the specific density of dry ice. (google search!)

Please note... the dry ice will sublimate to gaseous form... and will take up far more volume. Thus, the warning by an earlier mentor regarding expansion and pressure relief should be followed.

Good Luck !!!