I use Fleischmann's bread making yeast in a jar ... I can use the same jar
for at least a year and each batch is as good as the last. I use 2 cups
sugar, 1/4 tsp yeast and 1/2 tsp baking soda in a two quart (~ 2 liter)
plastic juice bottle. A batch will typically last about 3 weeks.

I actually have two bottles connected up via a "T" connector, and try to
swap out one every two weeks to have a consistent generation of CO2.
Sometimes I don't, though, in which case the mix will be nearly spent.
Because it usually takes about 24 hours for my new mix to get going (most
people report shorter times), I add some yeast to the existing mix to keep
it going until the new one is ready.

All of this means that I have a pretty worry-free, no-hassle DIY CO2 system.
Another thing that really makes things easy ... I have a pH controller which
operates an air pump to blow off excess CO2 when the pH gets too low.

For what it's worth ....

"Jon W" wrote in message
...
After adding a load of new plants to my 60cm tank a few weeks ago I
installed a yeast fuelled CO2 generator. This bubbled away happily for
about
10 days and the plants all seemed in good health, even my stoic old Java
fern started producing fresh green leaves.

The problems started when I tried to get a second batch going. The yeast
(which is Allinsons bread making yeast can be used for brewing according
to
the tin) has been kept in the fridge since it was opened. I have tried
everything to get a brew going but nothing seems to work. I have boiled
the
water and let it cool, left the yeast out for a few hours to let it warm
up,
made started cultures and added it to the body of the sugar solution.
Nothing has worked.

I'm sure the system isn't leaking at all and nothing has changed since I
made the first batch. The last thing I want is an inconsistent supply and
fluctuating pH. Does anybody have any advice or should I just admit that I

can't brew and leave my tank CO2-less? Unfortunately I can't afford a
pressurized system right now and all my new grow tube is growing is algae,
lots of it!