"Dave Millman" wrote in message
...
I was asked this question, and I'm not certain of the answer:

In a NON-injected plant tank, will diffusion of atmospheric CO2 keep up
with CO2 usage by plants, or is there a possibility that CO2 will get
depleted during the day, thus driving pH up?

The amount of CO2 in there in the first place is so small at 2-3 ppm that
there isn't much to lose & therefore very little effect can be had on the Ph
in reality.

PH does change with CO2 concentration so technically yes, if the co2 levels
get depleted to almost nothing then the PH will go up but not, I think by a
noticeable degree.

Besides, if that happened, because of the lack of CO2, it wouldn't be much
of a plant tank for very long!