Originally Posted by Rabbit
confusekid: Concerning what you said, its true that what you are looking for is a CO2 concntration in the water, but if the amount of CO2 being pumped in is greater than what you would've had otherwise, then its a net benefit. And since the water column can only hold so much CO2 (or any other gas at one time) there's no point in going overboard anyway.
What Im trying to say is that SOME CO2 is better than none and in this case, since the tank being used is relatively small, then it might actually still be more than the water can hold.
First, CO2 is far more soluable in water than other the atmospheric gasses your air pump will introduce. Long before you get to the point where you have "more CO2 than the water can hold", all the fish will be dead due to high CO2 levels or exremely low pH or both. Consider a soft drink. Water can "hold" a LOT of CO2. But you'll never get close to having to worry about that... See below:
Second, the thing that makes the CO2 go into the water is a process called diffusion. At the risk of being a little overly detailed... The rate of CO2 diffusion in water (or any other solvent/solute combination (not counting solubility))) is determined by 1) the concentrations of CO2 both in the "bubbles" in the reaction chamber and in the aquarium water and 2) the surface areas that are in contact with one another. The total amount of CO2 diffused also depends on the length of time the bubbles are in contact with the water. So, to maximize this diffusion, we want 1) pure CO2 bubbles; 2) little tiny bubbles in contact with lots of water and 3) keep these tiny bubbles in contact with lots of water for a long time. That's for a best case.
If you put an air pump in the yeast container and run the output into the tank, you're going to be pumping mostly "air" (a mix of mostly nitrogen and oxygen (and CO2 and other gasses in small amounts)) into your tank. Unless your yeast container is absolutely huge, the amount of CO2 the yeast will add to the "air" flowing out to the tank will be minimal.
You can find out just how minimal by hooking some tubing to a sealed yeast container, sticking bare end of the hose under water, and counting the number of bubbles it makes in a minute. For the sake of argument, let's say you count 10 (which is too high, but it makes the math easy).
Now hook your air pump up to the hose and do the same thing - count the number of bubbles the air pump makes. Probably around 10 a second or 600 in a minute.
So if you did your setup as you propose, you would generate a volume of mixed gas (mostly air) equal to the volume of 610 bubbles every minute. Doing the math, you will have increased the CO2 concentration in the "air" leaving the yeast chamber by 1.6%. Since the tank is open to the air, the concentration of CO2 in the water will be about the same as the concentration of CO2 in the air. So your trying to diffuse CO2 into the tank when the concentration of CO2 in the air your pumping in is only 1.6% higher than the concentration in the tank already.
With such a tiny difference in CO2 concentration (between the bubbles and the tank water) the rate at which the CO2 would diffuse into the water will be incredibly low. You would need to hold this air in contact with the water for hours and hours to transfer a noticeable amount of CO2. Given the rate that the air pump will run at, there's no way to hold that much gas in contact with the water long enough to do any good. The CO2 will come out of solution at the surface of your tank MUCH MUCH faster than you could hope to compensate for with this setup.
With conventional CO2 systems, you have bubbles of 100% CO2 (big difference in concentration equals fast diffusion) and these bubbles are held in contact with lots of water for a long time (hopefully until the bubbles completely disappear) so all the CO2 goes into the water. Put the same 10 bubbles a minute of pure CO2 into the reactor and hold them there until they completely dissolve and you ARE increasing the amount of CO2 in the water by an easily measurable amount.
Clear as mud, right?