Originally Posted by Unregistered
Understood: The atmospheric pressure will be ambient at around 1,000 millibars and the temperature will also be ambient at around 18 degree Celsius. The application method will be diffusion of CO2 percolated into the water at the bottom of the water column.
You may find this Wikipedia article relevant:
The current partial pressure of CO2 is slightly higher than what is indicated her, about 3.79 x 10^(-4) atm, so saturation would be about 550 µg/L. Your 200000 ft³ is about 5.66 ML, so 3100 g (3.1 kg) of CO2 would be contained at saturated conditions. Any extra will bubble off and tend to raise atmospheric concentrations.
This is based on the Henry constant at 25 °C. I didn't find any data on variation. It should be higher at lower temperature, but I don't know if the temperature dependency is anything like oxygen, which is tabulated vs temperature.