Note: Even using it fairly sparingly doesn't reduce it's effectiveness. It just takes longer to do it's job.

OFG brings up a good point - using Borax to neutralize the acid when finished treating. I had a case where treating cheap shorty fenders the acid seemed to continue working even after I rinsed and polished. I noticed a couple weeks later that it left dull specks down to the steel where the rust spots had been. I now rotate the old box of Baking Soda out of the fridge into my OA rinse baths to ensure the acid stops working.