Oxygen depletion

[john j]

That's difficult to calculate.  Would depend on the time, temperature, pH of the water, how much water was in the tank, the surface area exposed to the water and the pressure to name just a few of the important variables.

It would certainly consume some of the oxygen from the air in the tank.  It would not however, produce another gas as a byproduct. 

I could do a calculation that would estimate the amount of oxygen lost based on a given weight of iron oxidized, and the weight could be converted to a volume of iron, but I don't think that would help much because we would just be guessing at the amount of oxidization taking place in the tank.