CO2 in substrate: worth it?

> >charley (cbay at lookout_ecte.uswc.uswest.com) wrote:
> >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.  
> From: Bob_Hoesch at mail_fws.gov
> Bob Hoesch (Bob_Hoesch at fws_gov) responded:
> 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.

That's a good point-- most roots don't have stomatas for environmental
exchange :-).

What I was _hoping_ would occur is that I could inject CO2 into the
substrate and have the CO2 uniformly disperse up through the substrate
to all of the tank (I recall seeing a thought in this list a week ago
on injecting CO2 into a RUGF for a similar effect).  Because it would 
be in the substrate, I am hoping the longer suspension in the water 
would allow for more efficient CO2 utilization before loss through the 
water surface (it would start its travel to the surface from *below* 
the substrate, as opposed to the *middle* or *lower* parts of the 

So, even if the roots don't need it (they don't), it may allow for
better (more efficient) utilization, more even distribution, and 
possibly less agitated/varied addition to the system.

However, I am beginning to see some more issues I can't answer with 
this thought:

(1) With CO2 injection into the substrate, the pH will drop (possibly
dramatically?)  After all, we have a rather small area of water for
all the CO2 we want to eventually disperse through the substrate to the
rest of the tank, and our flow rate will be very low.  How low can the 
pH go without introducing other problems for the plant roots or 
bacteria?  On the other hand, if CO2 disperses so quickly (it's so 
soluble), could we use it to provide some sort of circulation?  Or, 
if it disperses so quickly, is the pH change in the substrate *not* 
so dramatic because it moves up through the substrate quickly?

(2) It's (I think?) slow to disperse through the substrate to the
main aquarium water.  Thus, getting the right setting may be difficult,
and each adjustment to the CO2 reactor would have to be followed by
a (significant) wait period.  Or, could this (assumed) buffered-delay 
be good to avoid violent pH swings...?

Of course, if part of the UGF is fed with the same water that goes
to the rest of the tank and the UGF gets the same PPM CO2 as the
rest of the tank from the CO2 reactor down at the pump in the trickle 
filter, then I don't see any problem (and probably no benefit) of the
small (and accidental) CO2 in the substrate.  This is what we're doing 

I dunno.  I haven't tried this.  Is CO2 injection into the substrate
worth pursuing?

cbay at lookout_ecte.uswc.uswest.com