I agree with mwsmith2....the 'acid column' is supposed to cause carbon dioxide to gas off much like pouring acid on baking soda causes it to fizz. I have even read descriptions of it that says you might see bubbles of CO2 form and rise to the surface but that just doesn't really happen. The problem with that is carbon dioxide is very soluble in water and unless you airate the water to drive it off it tends to stay in solution. Carbon dioxide in water forms carbonic acid (think club soda....exactly the same thing). To drive the CO2 off you shake the bottle of club soda (or airate your pool!)
hope this helps.