Locally man made ocean acidification is possible but if you consider the amount of ocean water (about 3.612 x 10²º gallons of sea water in the ocean)then I am no scientist but I strongly suspect the amount of man made carbon dioxide needed to change the ocean is way above what is currently being produced.
There should be a chemist on Free Republic who can do the calculations.
The important change is to the pH of the surface ocean waters (down to about 200 meters or so); this is a lot less volume than that of the entire ocean.
You could peruse this:
Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers