Originally Posted by rodekyll
1500 ppm, 5000ppm or 25000ppm -- how do you know, using yeast, a coleman lamp, or soda? There is no formula for these, and environmental issues such as air leaks and temperature would render a formula useless anyway. You could be completely out of the effective range with these methods, making your effort a total waste of time and money. You could also be damaging the plants. You are completely out of control. There's no way to tell without a monitor, and no way to start, limit, or stop the flow without a regulator.
Any way you look at it, the bottled co2 is the way to go.