Airpumps on DIY CO2 Setups
Some time back, someone asked about using an airpump to pressurize a DIY
CO2 setup. Another writer suggested that the potential to pump foam into the
tank is a good reason to avoid doing this.
A better reason to avoid it may be that it will make the CO2 system almost
totally ineffective. This is because mixing the CO2 with normal air will reduce
the concentration of the CO2 pumped into the tank.
The purpose of the yeast/sugar mixture in a DIY CO2 system is not just to
produce CO2. CO2 is already abundant in the air around the aquarium. This
CO2 in the room air dissolves into the water in the tank and the concentration
of the CO2 in the water reaches an equilibrium with the concentration of the
CO2 in the air.
We want more CO2 in the water than that. To get additional CO2 into the
water, you must produce a gas with a much higher concentration of CO2 than
that found in room air. This will alter the concentration equilibrium set up by
the room air and result in more CO2 dissolved in the water. The sugar/yeast
or CO2 cyclinder provides this highly concentrated CO2.
Given that most DIY CO2 setups produce a bubble of CO2 every second or
to, using an airpump that produces many, many bubbles per second will
reduce the concentration of CO2 until it is about the same as that of the air in
the room. You may as well dispense with the CO2 setup completely.
I'm surprised that the chemists etc on this list, who know more about the
subject than I, have not pointed this out. Is there something wrong with my
thinking on this? Check me out, please.