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O2/CO2

Chuck Gadd wrote:

>> C'mon, man, it's a scientific fact that O2 and CO2 are independent.
>> Chuck Gadd's experiment demonstrated this. You are wrong. Period.
>> Adding CO2 does NOT reduce O2.

Peter Aiken wrote:

>I am afraid it is you who are wrong. Gasses in solution are not independent
>of each other. 

True, but at the levels we are discussing, which is far below saturation
for CO2, it has always been my understanding that the amount of Co2 in the
water did not _significantly_ effect the amount of O2 that could also be in
the water.  That has certainly been my observation.

>Adding CO2 (or any other gas) to a tank will in fact reduce
>O2. This is expressed by Henry's law which states that the volume of a gas
>dissolved is proportional to its partial pressure. 

But are you taking into account the fact that O2 is also being added to the
tank at greater than normal atmospheric concentrations due to photosynthesis?

>By increasing the amount of CO2 from .03 to 5% you have decreased the amount
>of O2 by 15%. Adding CO2 to a tank does reduce O2, despite the proclamations
>of some "experts." That being said, the important question is whether within
>normal paramters for an aquarium the addition of CO2 can cause enough of an
>O2 drop to affect the fishes. I do not know the answer to this one, but it
>is a possibility.

>FWIW, I am a professor of physiology and I do in fact understand these
>things!

Then how do you explain the measurements that many of us with CO2 injected
tanks of O2 in the range of 11 mg/L during the height of the photoperiod?
This is way above saturation, and the CO2 levels at these times in my tanks
run around 25-28 mg/L, which of course is also much higher than normal
atmospheric equilibrium.

I would love to hear more from you, but I really suspect that like most of
the other posts in this thread, that you are telling only part of the
story. (we all do that from time to time)  The bottom line for me is that
in spite of all the mis-information and partial truths that have abounded
in this thread, the original poster is putting 2 and 2 together and getting
6.  There is more to his problem than the simple observations that he has
made. 

Karen