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Re:CO2 DIY idea

* From: Andrew McLeod <thefish at theabyssalplain_freeserve.co.uk>

.........Another (potentially) cunning plan...
Yeast in aerobic conditions, like most life, reacts sugar+oxygen--
CO2+water, which would actually be preferable as alcohol poisons yeast, and since alcohol is not entirely oxidised, the aerobic reaction produces significantly more CO2. However, it does not result in an increase in gas pressure, so it would only produce a CO2 enriched atmosphere, and not produce a flow of CO2 like an anaerobic reactor, but since (I am assuming) CO2 is more soluble than O2, a flow of water through the reactor or an air pump pumping very slowly from the reactor into a diffuser might allow CO2 enrichment.

I have had a similar idea like this for a year or so. My idea was to have a two or three liter soda pop bottle filled about 3/4 full with loose topsoil. The bottle would be stoppered with a two-hole rubber stopper and glass tubing would pass through one hole down to the bottom of the bottle. Air would be pumped in through this tube and pass through the soil and then go out a short glass tube in the other hole which would be connected to air line tubing that would send the air into the aquarium. Basically, the design is meant to circulate air through the soil and then into the aquarium. For CO2 production, I would mix into the soil a tablespoon or so of uncooked, dry oatmeal. An aquarium air pump would push the air through the soil much too fast, and and the percentage of CO2 in the air being pumped into the aquarium would be way too low. To reduce the rate of air flow, I would put a piece of glass capillary tubing in the line going to the bottle. This is glass tubing that is very thick walled and has a very small diameter canal down the center similar to that of a glass thermometer. You can get it from scientific supply companies with a variety of capillary diameters. With the right capillary diameter you should be able to get a flow rate that would raise the CO2 content of the aquarium considerably. You don't have to use yeast with this set-up. The fungi and bacteria and all the other critters in the soil will do the job. When CO2 production wains, just mix in some more oatmeal. (If you don't like oatmeal, you can use cream of wheat. Basically, anything starchy will do.) This has the big advantage, as Andrew pointed out, that the aerobic breakdown of the oatmeal is much more efficient at producing CO2 than anaerobic breakdown, and you don't have to worry about alcohol or other metabolic byproducts poisoning the system.

Somebody ought to try it. I haven't bothered because it is easier for me to breathe into a plastic bag and then pump the contents (about 4% CO2) into my tanks.
Paul Krombholz in sunny central Mississippi