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CO2 concentration and the Prandlt layer

Subject: CO2 concentration and the Prandlt layer

<Snip long discussion of the need for circulation in the planted 
tank>

> The question is then, how low a concentration of CO2 would be
> sufficient to maintain optimal growth? Remember that we need to
> provide above average growing conditions in an aquarium in
> order for the plants to outcompete algae. Ideally, we need a
> experimental study which attempts to quantify the results by
> the average surrounding water velocity (which can be measured
> accurately by pitot tube). We could presume adequate nutrient
> quantities and 20-50% of light saturation which might be typica
> of our HIGH lighting category of +4 watts/gal. (of course it
> varies for plant type; I suppose we'll get vastly different
> results studying H. poly than Anubias or Crypts)
> 
> I wonder if this might be the hidden factor in some of Dorothy
> Reimer's low-tech tanks without CO2 injection?

Nope.  Dorothy doesn't use power heads either.  As far as I 
remember, her filtration is via bubble-up corner filters.

> ------------------------------
> 
> From: "Peter Hughes (X)" <peterh at pican_pi.csiro.au>
> Date: Tue, 28 May 1996 10:04:43 +1000 (EST)
> Subject: Re: Aquatic Plants Digest V2 #101
> 
> > From: "Olive K. Charlsey" <achaudh at emory_edu>
> > Date: Sun, 26 May 1996 16:04:56 -0400 (EDT)
> > Subject: CO2 Bends
> > 
> > If you have read the article at:
> > 
> > http://www.cco.caltech.edu/~aquaria/Krib/Plants/CO2/co2-bends.
> > 
> > <snip>
> > 
> > I have played with some similar CO2 systems - they are not too
> > which is good - less chance of overdosing.  Today, I was talki
> > John Burleson (with Dupla).  I asked him about his reactors - 
> > efficient to use without a controller.  When I told him of the
> > idea (I am currently doing it with an eheim), he said there ma
> > problem because of the change in partial pressure as the co2 l
> > water exits from the filter.  He thought this caused the CO2 t
> > instead of converting to carbonic acid.  Neither one of us kne
> > to understand what is really happening, but he assured me that
> > discussed this with reliable sources and thought this is discu
> > one of Spotte's books.  The problem is that the dissolved CO2 
> > an embolism, like the bends for divers.  This may be a good to
> > the net.
> > 
> > <snip>
> > 
> > Then you may be able to answer my question.
> > 
> > CO2 does dissolve in water to form H+HCO3-. There is no other 
> > dissolves, no matter what pressure, no matter what the concent
> > 
> > So, what are they talking about in that message?
> > 
> > When the "CO2 laden water" comes out of the filter, it has a h
> > concentration of carbonic acid (H+ HCO3-) since there is no di
> > between dissolved CO2 and carbonic acid.
> > 	
> > Also, the water is not exactly "laden" compared to the rest of
> > tank water when it exits the filter. Certainly it has a higher
> > concentration, but really, not a whole lot more. 
> > 
> > Any thoughts? Am I missing something here?
> > 
> > 					Alok
> The same problem could be encountered in either case, you are dr
> increasing the partial pressure of CO2 in the reactor and the fi
> This causes the water to saturate and perhaps supersaturate for
> dissolvable CO2. The water then comes out of the reactor etc and
> the partial pressure drops and some CO2 may come out of solution
> bubbles. This would be worse if either was under extreme pressur
> pressure drop alone can cause this effect. 
> 
> There are two things which mitigate any concerns that I may have
> this. The first is that this would only occur in the water from 
> outlet of either the reactor or the filter and would be sudden a
> localised. It would rapidly reach equilibrium again. The second 
> never bother to use aged water in my water changes. During the w
> here the dissolved gas reaches high levels (gases dissolve mopre
> water) and during a water change this all comes out because of t
> change in temperature. It has not worried either my fish or plan
> single look at the health and colours of my fish is enough to se
> keep mostly Australian rainbows with a few Corydoras and a hill 
> loach, together with the obligatory SAE's. I have not had to tre
> tanks for any disease now for 2yrs and have not had a death in c
> except for 2 fish that were damaged by the fish catchers at the 
> 
> The problem would be nasty if the supersaturated water was insid
> fish and someting caused the gas to come out then. I have a bit 
> trouble envisioning this situation in an aquarium, but I am sure
> some of the inventive people on this list may think of something
> suddenly deliberately applying a vacuum to the tank).
> 
> Hope this helps
> 
> Peter Hughes
> 
> ANGFA ACT
> 
> ------------------------------
> 
> End of Aquatic Plants Digest V2 #103
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Karen Randall
Aquatic Gardeners Assoc.
Boston, MA