Go to any Petco and buy this tiny internal filter: http://www.petco.com/product/13796/H...er-Filter.aspx
In the box you will find everything needed to make an extremely efficent in-tank Co2 reactor:
1. Discard the tubing that supplies air to the filter and is meant for aeration, you don't need it.
2. Open the filter - as if your intention is to clean the sponge.
3. Remove the sponge from the compartment.
4. Pull and remove the green flow control slider.This leaves a small opening on the side of the filter.
5. Close the filter without the sponge. When doing that put the CO2 tubing in the small opening mentioned above. Basically 1/2" of the CO2 tubing is now inside the filter, right under the intake, and it's held in place by the closed filter.
6. The filter comes with a flow nozzle. Put the sponge removed in step 3 over this nozzle.
7. Attach the flow nozzle to the filter.
8. Peel off the technical info sticker. It's white and attracts the eyes.
Basically you have done two things:
A. Put the CO2 tubing under the intake of the filter.
B. Attached the sponge on the outtake of the filter.
When the filter runs the CO2 bubbles hit the pump impeller and make a very gentle noise. This is your bubble counter. Count the bubbles with your eyes closed if you want. You will have to get about a foot from the reactor though - it's hard to hear if you are more than 2-3 ft. away.
When the bubles hit the impeller they get broken into tinier bubbles. These tiny bubbles then get trapped in the sponge with 60 gph of water flow disolving them almost 100%.
The few fine bubbles that escape the sponge look like a tiny cloud. It consists of bubbles so fine that they have a hard time floating up to the surface. Even the most gentle side flow carries them to the side and around the plant leaves.
Old design of mine but this $10 filter really makes it possible to make an ideal internal CO2 reactor in literally less than 1 minute. The filter is very small (easy to hide), black (doesn't attract the eyes), and has a strainer that makes the suction gentle enough so snails don't get stuck on the intake, die and block it. Virtually zero maintenance.
Maybe someone could post pictures showing how to do everything I described. I haven't picked up a camera in many months but it seems that life still goes on as usual.