Bob_Hoesch responds to Charlie Bay

>     >I had thought that it would also be a good way to do CO2 injection 
>     >right into the substrate, but I now think that if I keep the 
>     >flow-rate low (like I think it should be), I won't be able to get 
>     >enough PPM CO2 injected into the substrate.  
>     I'm sure others will point this out as well, but CO2 is used only by 
>     the leaves, and then only when the lights are on.  Photosynthesis is 
>     the process whereby the carbon in carbon dioxide is "fixed" into 
>     organic compounds for use by the plant.  The energy provided by light 
>     is used to drive the process.  When the lights are off, plants respire 
>     (and use oxygen) as animals do.

I'm not exactly sure what your point is Bob. Are you implying that
CO2 is not taken up by the root system? My understanding is that
plants have at least three strategies for obtaining CO2. They use
free dissolved CO2 in the surrounding waters, they make use of
atmospheric CO2 when possible, and they obtain it through the root
system in the substrate. There, concentrations can be up to 100 times
that of the water. The carbon is stored as malate (malic acid) during
both the day and night, and converted during the day for use in 
photosynthesis. I assume that it is piped up to the leaves, just as
oxygen is  pumped down into the root system. I think that I read
this in Aquatic Botany some years ago.

The Optimum Aquarium is an interesting book, but I've always viewed
it as as sort of advertising brochure for DUPLA products. They gloss
over a few questions such as why the root system should have a
preference for warmth vis-a-vis the rest of the plant. I would have
expected the opposite. They don't really back up their statements with
measurements.They don't describe laterite or its functions so that
you could seek alternatives, nor do they tell you how to generate
CO2 cheaply. For that you have to go to the NET. They just tell you
what does not work. Of course the translation is atrocious. For this
reason I've never purchased any of their product, always seeking
cheaper alternatives.

As others have indicated over the last few days, David Webb's
approach to water movement up through the substrate, and Mr. Kelly's
successful experiment with clay, vermiculite, and pond tablets
seem to point in the right direction. I've accumulated all of the
ingredients and am presently looking for an appropriate clay.