You can buy carbon dioxide kits for aquarium use, and most of them have a diffuser or something like that to make the gas bubbles very small so they will dissolve in the water. The cheap carbon dioxide kits use a fermentation process to make gas, and the expensive ones with timers and stuff have pressurised bottles of CO2. Actually the 2 should be a subscript. If you want to raise some exotic plants, CO2 supplementation is almost required. However, if you're not careful with the stuff, it can drastically change aquarium chemistry and grow a bunch of algae. As for the breath of the humus bean, it does have lots of CO2, and it may be possible to add some to an aquarium by blowing through an air hose connected to an air stone. If the fish all come floating to the top, it's time to be more temperate in one's eating and drinking habits. Sorry, I just had to say that.