In addition to what was said on the Pool Forum, acetic acid (the acid in vinegar) is an organic chemical. You can consider it to be a chemical relative of ethanol. Since much of what we try to do in a pool is to oxidize organics introduced into the water, why on earth would you intentionally add more and have something else that can consume chlorine? There are a very few organic substances that we add to the pool and pretty much the only one that we intend to keep in the pool is Cyanuric Acid (and its chlorinated derivatives). Sometimes, when we have trouble with soapy films (and are impatient), we buy enzymes, and sometimes when we have metal in the water we buy a chelating sequestrant (an organophosphate), and when we want to reduce an iron stain we use ascorbic acid, but these are exceptions.
Richard