I'll check for the thread and post it tomorrow
What I mean is say the equilibrium level is 3ppm. (Will be lower in higher temps I suspect)
The water tries to maintain equilibrium at 3ppm it won't go above this level without us forcing it in via injection. When the plants use CO2 the level drops and the water tries to return to 3ppm. When we disturb the surface the CO2 won't be lost because it is already under the equilibrium. The agitation just gives the water a faster route of returning to the 3ppm. At night it doesn't really matter. The plants produce CO2, the water expells the amount over the 3ppm.
Therefore what I am saying is that with agitation we maintain the 3ppm because the 'added area of water surface' brings the amount used by plants back in quicker. In much the same way as we bring more O into the water by more surface turbulence.
Cool

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No, the equilibrium level is still 0.5ppm, and adding surface agitation will only bring it towards that.
The reason non-sterile water has more is because of the bacteria and other organisms respiring. Take a sample of pond water with 3ppm of CO2, shake it around for long enough for CO2 to diffuse, and it should go back down to 0.5ppm. Wait a bit for the organisms to respire more and it should go to 3ppm again.
The organisms are in effect "injecting" CO2.
Of course that would need to be done with a CO2 analyser

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I would suggest the amount of CO2 created by fish (unless its a 20x overstocked ebayer's tank) would be absolutely minimal in comparison to the 3ppm equilibrium level.
In my pretty new very lightly stocked shrimp set up with quite high lighting, I was finding 5-8ppm CO2 by the end of the day. In my heavily stocked and heavily planted with medium lighting corner tank I can get anywhere between 8-15ppm by the end of the day (depends on if the power head breaking the surface is working). Before I added the power head and air pump, CO2 levels were even higher than that.
Its not just the fish, it's the bacteria on pretty much every surface of the aquarium, in the substrate and in the filter breaking down waste.
Like I said in the other thread, levels would vary from tank to tank, but as long as they are above 0.5ppm, surface agitation is working against the plants.
While I don't trust those levels to be very accurate, I used two different test kits (Aquasonic CO2 test kit, and a pH/KH cart using a Nutrafin KH test kit and an API pH kit) and the results were similar so I don't think they are that far off. The pH/KH chart result was much higher than 15ppm because I have soft ~ pH 7 water from the tap, and I'm guessed the bogwood in my tank was skewing those results, so I just used the lower results from the other test kit (which I used several times to make sure I was getting consistent results).
Some reading for your amusement
I'd like to find out what it takes for plants to go into CO2 limited mode, is it literally 0ppm? Or is it just low concentrations low enough so that it's harder for the plant to scavenge for the CO2, like maybe 3ppm? Obviously it would depend on species, and it may not be bad for some if they can use other carbon sources well.
But regardless, surface agitation still doesn't make sense to me yet unless the CO2 is below 0.5ppm, which to me thus far seems very unlikely in our aquariums.
lets just hope Tom reads this
I hope Tom does read this, I think I might also PM Bignose to see if he has any thoughts on the subject, chemistry seems to a strong point of his

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