academic meanies and snow-melt in substrate.

> (1) When the water is still, is the CO2 diffusing in faster than the O2 can
> diffuse out?  It would seem so, because of the production of bubbles. 

Both oxygen and carbon dioxide diffuse in still water.  

> bubbles for that reason, alone.  However, I am pretty sure that CO2 also
> diffuses faster, because it can diffuse in several forms (dissolved CO2,
> carbonic acid, and bicarbonate ion).  Chemists: back me up!  I'm too old
> and feeble to look up solubilities and diffusion rates.  Thanks.

I actually think it is the other way around, diffusion coefs for CO2 will 
be lower because those ions are more strongly hydrated than oxygen.
> (2) when the water is moving over the leaves, shouldn't it allow the CO2 to
> diffuse in even faster than it was before?  And, if this happens, wouldn't
> you have an increase in O2 production, and still have production of
> bubbles?  My hypothesis is that photosynthesis was already CO2-saturated in
> the stagnent condtion, and so increasing availability of CO2 by decreasing
> the boundary layer did not increase the rate of photosynthesis.  

But increasing the flow rate will also carry away oxygen more readily, so 
it isn't a good test to compare bubble production in stagnant and 
moving water conditions.

> You all get a B because I have a reputation as an academic meanie to
> maintain! :-(


> I wouldn't add KHCO3 and CaCl into the substrate. A slightly acidic
> substrate is fine; you don't want it to rot. 

CaCl2.  It doesn't matter if you add these two chemicals to the substrate 
or in the water column, they are both freely soluble and are going to 
wind up wherever they want to be in a few minutes or hours.