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[APD] RE: CO2 off at night

>>Why do we all of a sudden think "20-30 ppm" of CO2 is a good range?  I've
using a maximum of 15 ppm since 1987 with more than enough plant growth. Or
does that go along with "4-5 w/g" of light? People, people, people, more is
better. All things in moderation.<<

Here is a quote from David Huebert, (wasn't he at one time one of the old
masters here?) From his Water Plants 101 article

 "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."

I thought 30 mg/L equaled somewhere between 20 and 30ppm. Is it lower than

Robert Paul Hudson

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