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Re: CO2 system with/without pH controller

Peter G. Aitken at peter at pgacon_com wrote:

>> C'mon, man, it's a scientific fact that O2 and CO2 are independent.
>> Chuck Gadd's experiment demonstrated this. You are wrong. Period.
>> Adding CO2 does NOT reduce O2.
> I am afraid it is you who are wrong. Gasses in solution are not independent
> of each other. Adding CO2 (or any other gas) to a tank will in fact reduce
> O2. This is expressed by Henry's law which states that the volume of a gas
> dissolved is proportional to its partial pressure.

I believe George was referring to the relationship between O2 and CO2 when
both are *in solution*. Henry's law pertains to the relationship of a
dissolved gas in proportion to its pressure in a gaseous state. In fact,
Henry's Law actually proves that George is right, since the addition of CO2
to water does not change the concentration of O2 in solution.

> At equilibrium, water will contain these gasses in the
> following levels:
> Suppose then you add some CO2 to the system so that the
> air now contains 77% N2, 18% O2, and 5% CO2. The total pressure remains the
> same. The water will now contain the following:
> N2 585.2 mm Hg
> O2 136.8 mm Hg
> CO2 38.0 mm Hg

Since CO2 is being added to the water via a pressurized tank, the partial
pressure in the atmosphere has little to do with it. Unless you change the
partial pressure of the O2 in the air above the water (which isn't gonna
happen in someone's house where their aquarium is), its concentration in the
water will not be affected by the addition of CO2 via a pressurized tank.

Dan Dixon