> I was wondering if anyone has tried this with home-brew "yeast CO2"
> injection.snip
Hi Johnnie,

I am having about three months experience on DIY yeast CO2 and IMO best
results I had is to direct the tube from bottle direct into power-head
outlet. Because my pump hasn't an air intake, I applied on output a 
Fluval Venturi device and I inject CO2 by it. The matter is to dissolve
as much possible CO2 in water. First experiments was to simply
bubble under a plastic bell on top of water, but was ugly to see, and
I don't love to see many fixtures into tank :-(
Now I am working with two 3 liters bottles we normally use here to
conserve fruit or legumes at home. Matter is that I had lot of problems
with plastic bottles all due to thery little leacks, but usefull to
compromise the CO2 bubbles. My bottles now are all glass-pyrex and the cover 
is squeezed against bottle throught a lever and has a large rubber seal.
On glass cover (pyrex) a glass-working-shop made a hole of 6 mm and I locked
into with resin + silicon a little straight connection.
The bottles are charged every 15 days and now all
works wonderfully. Only extra maintenance is at every bottle rconditioning to clean
the CO2 outlet into ventury (just scrapping with a little wire) where normally
is forming some biological white paste. On past mails on net people well explained
that this is a natural reaction with no pain at all for aquarium equilibrium.

May be that the system of pumps you are proposing will work but IMO starts
to be complicated (you are managing a gas); but I am curious to read something
more on net.

Will appriciate to know in future your experience. TIA

p.s.: best is to apply the Venturi on bottom of tank just lied on gravel to
permit to CO2 the maximum of dissolving possibility.
Ciao  Ezio                     _ _
___________________________,,,_o o_,,,________________________
       FERRO Ezio               -        Torino - Italia  
Quando il gioco si fa' duro,        When the going gets tough,
e' il duro che inizia a giocare.    the tough get going.