Re: Aquatic Plants Digest V2 #224


> Aquatic Plants Digest    Saturday, 28 September 1996    Volume 02 : Number 224
> ----------------------------------------------------------------------
> From: "David W. Webb" <dwebb at ti_com>
> Date: Fri, 27 Sep 1996 15:52:05 -0500
> Subject: Re: Airstone anathema
> >From: Elizabeth Worobel <eworobe at cc_UManitoba.CA>
> >
> >To suggest that airstones are somehow 'bad' for aquatic plants is wrong, 
> >wrong, wrong (to repeat a recent post)! There is clear research which 
> >indicates that photosynthetic rates in aquatic plants increase with 
> >increased rates of aeration ... the reason is that increased aeration 
> >increases water movement and therefore decreases the thickness of the 
> >boundary layer. It is this boundary layer which is the limiting step in 
> >CO2 acquisition so the thinner it gets, the faster the uptake of CO2.
> The research I've read indicates that water flow increases photosynthetic
> rates, not aeration per-se.  It's relatively easy to set up a tank with
> plenty of water flow to decrease boundary layer thickness without using
> aeration.  Dupla recommends a swirl-pattern with a vertical axis down the
> midpoint of the tank.  I've done this on two tanks now and get very good
> plant growth with very little surface interaction and no aeration.  Plans
> for this type of system are on the Krib for viewing.
> >Airstones also do not 'drive' off CO2 ... they will equilibrate all the 
> >gases in the tank to atmospheric levels, nothing more, nothing less. This 
> >idea likely got started by proponents of CO2 injection who couldnt stand 
> >to see their CO2 levels drop even slightly ... in fact in most cases CO2 
> >injection is unnecessary. 
> Since in an aquatic system without a great deal of surface interaction, CO2
> levels tend to build up to higher levels than if aeration, waterfalls, etc.
> are introduced, it can be argued that aeration does drive off CO2.  The
> point of discrepancy lies in what's considered 'normal'.
> >There are only two instances where it is 
> >beneficial ... the first is when there is a daily fluctuation in pH which 
> >indicates that the demand for CO2 by the plants exceeds the abil
> >ity of the water to absorb it (of course in this case aeration will also 
> >work) ... the second is when growing plants which are unable to utilize 
> >bicarbonate (about half of aquatic plants have this ability).
> In your first case, aeration will help.  CO2 injection will help a lot
> more.  CO2 injection will also prevent biogenic decalcification in tanks
> like mine that don't get frequent water changes.

	Why would aeration help?  From what I've read, aeration tends to
	raise pH (though I haven't yet read an explanation as to why)  and
	pH fluctuation in a plant tank already means a rising ph in the
	day.  Could you explain this one a little more fully? Thanks!
> David W. Webb           Enterprise Computing
> Texas Instruments Inc.  Dallas, TX USA
> (972) 575-3443 (voice)  MSGID:       DAWB
> (972) 575-4853 (fax)    Internet:    dwebb at ti_com
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