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Re: CO2 ppm in tank

On Thu, 28 May 1998, Paul Nicholson wrote:
> The number of 20 or so PPM of C02 sticks in my mind as what I've seen
> thrown around as target level for a planted tank. What is this
> concentration as expressed relative to the ratio of air in the tank. Or to
> say in another way, what is atmospheric concentration of C02 that would
> produce a 20 ppm level in water in a system in equilibrium, assuming no
> production or consumption of CO2.

CO2 is only about 0.03% of "normal" dry air, and water in balance with 
air will contain only about 0.42 mg/l of CO2 at 25C (about 77F).  That 
number drops noticably as temperatures increase.  A concentration of 20 
ppm CO2 is 48 times the atmospheric balance point; it's what the water 
would balance at if the air contained about 1.4% CO2.

In an established aquarium without much photosynthesis going on, I think
CO2 concentrations are typically 3-4 ppm - higher than the concentration
that would balance with the atmosphere.  The value is higher because of 
CO2 from respiration in the tank.

Roger Miller