You only need to put in enough to get your pH down to the 7.0 mark. Alk is related to your pH. As you drop pH, the alkalinity will drop. Areating brings the pH back up so you can add more acid. Conceivably, you could areate and keep the pH down in the 7.0 range and your alk will slowly drop off. It just takes a while, that's all.

Michael