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Re: CO2 and low light

Mike <grace005 at gold_tc.umn.edu> wrote:

> So...let me see if I have this straight.  In a tank with no added CO2
> there is approx. 2ppm CO2, give or take a bit, right?  Let's assume the
> tank is moderately planted (50-75%) with typical low light plants such
> as Java fern, Java moss, Bolbitis, Anubias, and Crypts at 1.5 W/gal
> lighting.  In this scenario would the plants really only consume 2ppm
> CO2 or less during photosynthesis?  If so, then I appreciate your
> point.  But...let's say you are correct and they only need 1.5ppm. 
> Wouldn't it be harder to "find" that 1.5ppm when there is only 2ppm
> available, as opposed to say, 10ppm?  Afterall, in a high light tank we
> certainly are injecting much more CO2 than the plants actually need. 
> Anyone with data or experience?  If this non-scientific point of view is
> way off, please set me straight.
My point of view (also non-scientific) is that, if plants are living 
below their compensation point, the amount of CO2 in the water is meaningless.
They would perform in the same way with zero or 100 ppm CO2 in the water, 
because all the CO2 they need for photosyntheis is already in their tissues,
product of respiration. Nothwhitstanding, of course, the effects mentioned 
by Roger Miller on the amount of CO2 actually changing the compensation point. 

> Also, the tap water pH in this area runs about 8.0 to 8.4.  CO2 would be
> a nice way to bring it down some, and the expense isn't really an issue
> here.  So far It doesn't sound like anything "bad" will happen, or for
> that matter, anything "good".  Lowering the pH to slightly acidic would
> at least provide nitrogen as ammonium, as preferred by plants, correct?
Yeah, IMO CO2 is a good, perhaps the best, way of bringing down pH.
Provided, of course, a moderate value of kH.
> Thank you for your feedback!
> Mike

You'll welcome,

-Ivo Busko
 Baltimore, MD