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RE CO2 and sources

Roger Miller wrote:
"And for Scott and all discussing the source of CO2 in the aquarium...

The concentration of CO2 in aquarium water is typically quite a bit
higher than the CO2 concentration that would be present in the water at
equilibrium with air.  Therefore CO2 diffuses *out* of the water, not
into it.  In the absence of added CO2, the CO2 in most aquariums
originates largely from respiration in the aquarium.  Fish food would
the most prevalent source for the carbon, though some would also
originate from the biological decomposition of an organic substrate or
plant detritus.

If plants are using more CO2 than respiration provides in the tank then
the CO2 levels can drop below atmospheric equilibrium levels and CO2
will enter the tank water from the atmosphere.  That (in my experience)
requires a lot of light, can drive the pH > 9 and result in an
environment that is hostile for most plants. 

Roger Miller"

I think you missed the point that several of us were trying to make. 
Mine was that it had to come for the air or organic processes in the
tank.  I was later corrected that the air had to little CO2.  There was
some argument about that between a few folks but I think everyone
settled on the air having too little.

A couple of us got into the meaning of equilibrium -- I don't think
there was any actual disagreement--we were just being facetiously
detailed (or perhaps minutely facetious).

Truth is, I'm not sure where this CO2 thread is going but I think
everyone agrees that the air has too little CO2 to be a source for the
levels in (non-injected) aquariums.  My earily point about the air,
which was soundly corrected, was that the water achieves equilibrium
with the level of CO2 in the air unless more is added from another
source.  The correctdion was that the level of CO2 (in water) is higher
than the air.

The source of the CO2 in water, not at all uncanny, is not the air
then, but organic processes or tanks of CO2 (or sometimes volcanoes if
I remember the posts correctly) ;-) .

Does anyone still disagree with that?

Scott H.

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