[APD] Re: 20-30ppm CO2

[Thomas Barr <tcbiii at earthlink_net>]

> "At air equilibrium, the concentration of CO2 in air and water is
> approximately equal at about 0.5 mg/L. Unfortunately, CO2 diffuses about ten
> thousand times slower in water than in air. This problem is compounded by
> the relatively thick unstirred layer (or Prandtl boundary) that surrounds
> aquatic plant leaves. The unstirred layer in aquatic plants is a layer of
> still water through which gases and nutrients must diffuse to reach the
> plant leaf. It is about 0.5 mm thick, which is ten times thicker than in
> terrestrial plants. The result is that approximately 30 mg/L free CO2 is
> required to saturate photosynthesis in submerged aquatic plants."

Saturation for PS _depends_ on intensity of light.
Low light tanks will need less, also less nutrients etc. Everything is
scaled down. 

Many folks have loads of light these days. I give good high ranges for CO2,
NO3, K, PO4, traces, so called maximum ranges where folks with high light
set ups will NOT run out of something.

Having more of these nutrients/CO2 than you need at lower lighting doesn't
hurt, but you can get away with more variation with less light.

So what that "Pirate of Rockies," a keeper of Gaudy Dinner Plate fish (as
one eloquent individual said recently) was saying is quite correct for him,
Paul and Kevin's work with PMDD and folks that have tanks in the 2w/gal
range or slightly less. CO2 of 15ppm is fine for them. Most of them also
don't use DIY which can be 15ppm of CO2 and then trail off weekly down to
7-10ppm etc. Gas tank sources are more stable at lower dosages. It's tough
to narrow your CO2 down to 5ppm + or - with a normal test kit, a pH monitor
is more precise but there's still some play.

Many folks seem to miss that part of the PMDD approach, most of it was based
on lower light tanks, 1.6-2/w/gal of NO FL's.

If you want more light, you'll need to add more CO2/NO3/PO4 etc.

This led to being able to see the NO3, PO4 rates being reduced at high
light/CO2 levels and back tracking we applied these same higher levels to
the low light tank, often yields very nice results. You would not see this
uptake so well at low light.

But jumping to 3w/gal -5 w'gal of PC lighting with nice reflectors etc, now
suddenly you need more CO2, more(frequent) dosing of NO3/PO4/Traces etc.

I see no reason to dispute George's 15ppm when it's at these intensity light
levels. He's right about it.

...but having said that I also think the richer CO2 is not going to hurt
either.

Regards, 
Tom Barr

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