CO2 injection

Todd March wrote:
>Someone also recommended some "bell" (?) reactor made by Tetra?

I cannot speak for or against the  Tetra bells, but I found the following:
In Bernd Greger's "Aquarium Pflanzen", Kosmos, 1991, I found an
alternative to bubbleing CO2 into a filter. It is similar to the
Tetra diffusion bells but cheaper and more flexible. And you can
DIY. BUT it doesn't give values for soft water.
Greger uses a 3 cm (1 inch would do too) high inverted U-shaped channel 
into which the CO2 is bubbled. The channel is made out of glas or 
plexiglas strips, siliconed together, plus two end caps. The whole 
thing can be attached anywhere in the tank.

The dimensions are calculated as follows:
KH Value    Contact area (cm2)     Channel dimensions (example)
   10  dKH      30 cm2                 10x3 cmxcm
   11           50                     18x3
   12           70                     25x3
   13           90                     30x3
   14          110                     40x3
   15          130                     45x3
plus 20cm2 for each additional 1 degree increase in kH.
These values apply to 100 l (30 USgal) tanks. For a 300l tank, 
multiply by 3.

Although, most of you don't have near the 10 degrees kH, I decided 
to reproduce the whole table anyways for completeness sake.
Unfortunately, he doesn't give values (or a formula) for our low KH
tanks and since I don't use this myself, I leave it up to you
to figure out how much contact area you need. 
I guess that by adding some sort of sliding divider into a 20cm x 1cm 
channel, one could fiddle with the contact area until the pH is at the
desired level.

Three additional notes:
1) By bubbleing the CO2 below the channel into the water, you can then 
easily monitor the output of your yeast system. (natural bubble counter)
2) The channel needs to be "burped" periodically to vent other gases that
accumulate over time.
3) This could be a nice set up for a no filter tank.