>IMO the best way to dissolve CO2 in water is to use a box placed upside down
>on top of the tank (something like a diving bell).
I have using a method something like this and it works well, here it is:
HOW I MAKE IT
1. cut 2 large holes opposite of each other into the sides of a small coke
bottle, one slightly higher than the other. Poke a small hole just above the
upper large hole.
2. place some gravel into the bottom of the bottle to sink it. The higher
hole (the intake) should be positioned just infront of the filter outlet.
3. drill a hole in the cap and insert an airline, seal the puncture with
4. connect a "T" joint into the airline nearer the tank, so that the bottom
of the "T" is connected to a valve (the purge valve)
5. fit the other end of the airline to your CO2 generator bottle.
HOW IT WORKS
1. CO2 enters the reactor bottle and occupies the top of the bottle, which
forms an air bell.
2. water emerging from filter outlet enters reactor through higher hole and
exits from lower hole. The difference in hole height causes a great deal of
turbulence on the water/CO2 surface, allowing CO2 to dissolve into water
3. CO2 dissolving into the water is accompanied by air dissolving into the
CO2 bubble, thus diluting the concentration of CO2. Eventuallly an
equilibrium composition will form. The small hole above the intake will
allow excess air to escape.
4. if the CO2 supply needs to be shut off temporarily (eg. at night} the
purge valve can be opened. If there is a need to purge the air bell, loosen
the valve on the purge line and the gas in the air bell will rush out. Close
the valve and let the CO2 fill up again.