I found a simple to make, cheap method to costruct a power CO2 reactor
for 2$ plus the cost of a small power head. You can buy these small
part's holder's at OSH/ Orchard's supply called viewtainers which can
have the hold needed for the power head melted into th side or you may
cut a small hold for a snug fit pointing the power head downward from
the top. The venturi is connected to about 2 inches below the top of
power reactor to small hold for venturi action of the CO2 when it
builds up to this 2"(or any height you desire) size before it begins
to waste the CO2 as a mist.

This is essentially what I sold as an internal but this is out of soft
acetate plastic and is easy to work with.

You bubble the CO2 in from the bottom and this acts as a bubble
counter.
A lighter can be used to burn a hold into the plastic if you want a
side position for the power head or to make holds for suction cups for
top mounting of the powerhead.

I'll post some pics later, but at 2$, it works as well and is slightly
smaller than anything else and if anyone can beat the price, well, you
might want to sell them.

Here is the part:

http://www.viewtainer.com/

You can use my old design or copy other internals off the web. Most
DIY'er get the idea with these pics.

Adding the venturi loop will help increase the efficiency when you
need it and waste CO2 when you don't when the tank has already built
up to saturation levels of CO2.

These work very well and are easy for the beginner to use and are also
very good for DIY CO2 users, add a small hole(3/16") opposite the
power head side or about 2.25" down if you use the venturi loop at 2"
for burping when the power head is shut off at night(for semi
automatic control).

Holes to make:

Hole for the power head inlet(Make it smaller than the powerhead's
pipe outlet, then use a lighter to make it slightly smaller so you can
get a very snug tight fit/silicone it/epoxy etc)
I like the side mounting personally but top mounting can be done and
you will need a sponge to prevent the water from flying out oif the
bottom or you can use an elbow(better))

3/16" for venturi loop 2" down from top
3/16" burp hole 2.25" opposite venturi
3/16" CO2 "in" on top of tube for CO2 bubble input(you may wish to se
a 4" piece of rigid 3/16" airline tubing for this

Hey, it's 2$ and you can try it.

Regards,
Tom Barr