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Re: air/water CO2 exchange

> From: ruddigar at home_com
> Subject: air/tank CO2 eq'b
> To fix my super high CO2 problem

	What makes you think you have one?  From reading your last
posting, I think that you don't.

> I am heavily aerating the tank, thus
> diving off CO2, right?  However, the plants are bubbling away.  At first
> I thought it was just stray bubbles from the airstone or powerhead, but
> no - the plants are actually pearling.


>   My educated guess would be that the CO2 was probably driven off pretty
> quickly, and now instead of CO2 escaping the water, it is now dissolving
> into the water to create equilibrium with the partial pressure of CO2 in
> the air.
>   What I mean is that when we aerate the, we create surface agitation. 
> This agitation allows for faster gas exchange between the air and water.
> When I started the aeration, pCO2 was higher in the water than it was in
> the air.  This kicked the dissolution of CO2 from the water into high.
> i.e.  CO2 water -(fast)--> CO2 air
>   Therefore in a short time pCO2 in the water will be less than pCO2 in
> the air.

	The aeration speeds tranfer _both_ ways.  It helps attain
equilibrium more quickly, but you can't drive pCO2 in the water _lower_
than pCO2 in the air by more aeration.  More aeration will always drive
the two closer together. 

>  Furthermore, the plants are using CO2, creating a larger
> gradient between air and water.

	Yes, they will cause a gradient.

>   Now I believe that CO2 is dissolving into the water, from the air, and
> feeding the needs of the plants.  

	If your CO2 system is turned off, then that (and the
fish) is where the CO2 is coming from.

>   So ... what I would like to know is:  Should I just keep up this heavy
> aeration instead of hooking my CO2 back up?  Will this supply my plants
> with ample CO2.  I believe it will work, but I have no experience, which
> is why I'm asking the question.  Has anyone tried it?

	Just use tap water and CO2.  Stop confusing things with other

Paul Sears        Ottawa, Canada