Mineral acids will reduce alkalinity, but are very dangerous to use and will reduce the pH.
This article goes into more detail as to how this works:
http://www.freedrinkingwater.com/wat...nity-water.htm
From this article:
"The feed of a mineral acid will neutralize the alkalinity of a water. Hydrochloric acid, sulfuric acid or a combination of these can be used. This process converts the bicarbonates and carbonates present into carbonic acid. At this point, it is advisable to provide some method to permit the resulting carbon dioxide gas to escape into the atmosphere. The disadvantages of this acid feed technique are obvious. There are needs for precise control of the process and caution in handling the strong acid."