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C-OH no-Two! (continued discussion)

Just thought I'd keep this one going on...

>One question first:  Why would anyone put a tightly sealed cover over
>their tank?  I personally have never seen a pond or lake in the wild
>covered in this manner.  Maybe there is a reason I don't know of.  If
>please tell me.

Though not from personal preferences, reasons for a tight lid:
    Keep things out (dust, algae spores, cats...)
    Keep things in (fish, CO2)
    Keep water level (read water chemistry) constant

>Now, back to my theory.  The law of partial pressures states in a
>nutshell, "The gasses in a given container will be evenly distributed
>through out."

Dalton's Law (Partial Pressure Law) says "The pressure exerted by a
mixture of perfect gases is the sum of the partial pressures of the

definition following:
partial pressure-the pressure that an ideal gas would exert if it
the container alone.

>We know that in a tank with fish, enough O2 exists to support the life
>of the fish.  The evidence is obvious.


>So, if the CO2 dissipates out of the water, then so should the O2 and
>whatever other gasses are present in the water.  thus the layer above
>the water in a tightly covered tank should be made upof the same gasses

>in the same proportions as in the water, all equaly mixed.

Hole in logic above.  Just because one gas leaves the water doesn't mean

that all the gases will start.  Back to solution theory... Make some
put in sugar until no more can dissolve.  Let stand for two weeks.
Sugar will
have started to fall out of solution (crystallize) but the red coloring,
flavoring, preservatives and citric acid will remain in the solution.

Which gases are absorbed and released from the water in the tank depend
the concentrations with respect to the solubility level.  If I'm not
close to saturation
of O2 in the water and I start bubbling CO2, it won't cause a
considerable change
in the O2 levels (barring plant production of O2.)

>now that only leaves to assume that since the gasses in the water are
>able to support life, then the accumulated gasses will support life

This may be true, but most likely isn't.  Only if you create an
atmosphere above
the tank with the proportions of the solubility of the gases in water
will this be
remotely likely to occur.  For instance, air is about 79% Nitrogen 20%
and .6% CO2.  While all three can be found dissolved in the water, they
not be necessarily in that proportion.

There is a number called the partition or distribution coefficient.
This number
is the % of a substance in one phase (gas) divided by the % found in the
phase (water.)  Each substance has it's own coefficient for each pair of
when an equilibrium is reached.

Sorry for the long post of garbage that most didn't want to see again or
for a first time.  If you still have questions or problems, e-mail me
and I'll try to
help you understand.

I assume no responsibility for headaches caused by the above.
Douglas Bertelsen
dbert at umr_edu