I use the same method but run it into the tank straight through a fine
airstone. It also seems I can vary the reaction rate by changing the
amount of yeast used.
For anyone attempting this method, there are a few precautions when
you start out. CO2 will drop you pH!!! If you're not buffered up
enough you can easily wipe out an entire tank. The time to really
check the effect this DYI method of CO2 injection is having on your pH
is just before the lights first come on. Plants do not use CO2 at
night so the CO2 levels will be at their highest before the lights
come on. Too much CO2 going in without enough buffering can swing your
pH and stress or kill your fish.
I learned this the hard way when I first began using this method and
thought I'd warn folks to start slow and monitor what effect you're
having. With a little forewarning you shouldn't have to wipe out a
tank of fish to learn this :~)
Later
Cary Hostrawser
Minnesota Aquarium Society
http://www.mn-aquarium.org/
Rainbowfish Study Group of North America
http://home.earthlink.net/~sbuckel/index.html