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Re: Aquatic Plants Digest V2 #584

> 	Some people seem to believe that CO2 injection is a requirement
> for a brightly-lit tank.  This notion is based on the quite reasonable
> assumption that with enough light (say, more than 2.5 Watts per gallon),
> the plants are trying to photsynthesize too rapidly for the level of CO2
> normally available in a non-CO2-injected tank.  Thus, there is an
> imbalance, and various attendant problems.  However, I have also seen
> claims, some from dr. dave in his refreshingly blunt fashion ;-), that in
> most/many situations, CO2 injection is not necessary.  These claims say
> that in effect, we can compensate for lower levels of CO2 by, well, let's
> call it,"making CO2 more accessible."  So, instead of getting more CO2 to
> the plants by increasing CO2 concentration in the tank via CO2 injection,
> we work with the CO2 levels we have, and simply make it easier for the CO2
> to be taken up by the plants.  Plants have a boundary around their leaves
> (Prandtl boundary) which makes it difficult for gasses, such as CO2, to
> diffuse through.  (Why do they have this boundary, btw, if it actually
> makes it more difficult to access CO2? dave?)  What we aquarists can do,
> is disturb this boundary with a good current, thus making it easier for
> CO2 to diffuse through.  Hence, something like a good powerhead blowing
> through our miniature jungle, can solve our problem.  "Or, we can even
> employ a bubble wand or something of that nature.  True, the bubble wand
> will perhaps lower the CO2 concentration (if the tank is heavily populated
> enough with fish to have a CO2 concentration higher than its natural
> equilibrium with the atmosphere), but the increased diffusion rates more
> than compensate.
> 	Now, the above is meant to be only a summary of what is actually a
> wonderfully complex process, but I hope so far I have not made any basic
> errors in fact or theory, since my question assumes the above is
> essentially correct.
> 	I have a 20 long that I plan to convert into a lushly planted
> tank.  (Once I get the pink gravel out of there ;-) ....don't ask). Given
> that the tank is fairly shallow (12", I believe), do my fellow APDers
> think I would run into trouble w/out CO2 injection if I were to install a
> hood, painted white on the inside, w/ a total of 70 watts of T-8 lamps?
> These would be two 2' 18w 6500K, and two 2' 17w 4100K or 5000K.  I was
> hoping to simply use a good current via a powerhead to blow across plants,
> plus keep the Aquaclear 200 currently filtering the tank.  How about with
> one lamps less, for a total of 52/53 w?  Oh, and I should also mention
> that I plan to have floating plants as well, probably Salvinia.
	I should also add that my water is naturally very soft (KH 0-1),
so presumably more CO2 is present.  I have, however, been boosting the KH
up to 2-3 lately, to promote pH stability, a stability difficult to
achieve in soft water with a relatively heavy fish bioload.

> 				Andrew