Re: Barret's low consumption CO2 system

Diffusion between gas mixtures and water gets a bit complex.  I remember a
lecture I had in college about a diving beetle that dives down with an air
bubble held by waterproof hairs that cover most of its abdomen.  The beetle
does not simply exhaust the oxygen in the air bubble  and then return to
the surface for more air.  As the oxygen content of the bubble drops, more
oxygen starts to diffuse into the air bubble from the water, where the
partial pressure of oxygen is now higher. The beetle would be able stay
down indefinitely, using the air bubble as a gill, except for one thing.
Since the oxygen content of the bubble is lower than that of the water, it
also follows that the nitrogen content of the bubble is higher.  So,
nitrogen diffuses out of the bubble into the water, and the bubble gets
smaller.  Eventually the beetle has to go to the surface because its air
bubble is almost gone.

So, if you have a layer of CO2, trapped under plastic, as CO2 diffuses into
the water, nitrogen and oxygen will diffuse from the water into the bubble.
At equilibrium, the bubble will probably be a good deal smaller than it
was, but it will have the same composition of gasses that are dissolved in
your water.

Paul Krombholz