Actually, so long as you are not using calcium hypochlorite to chlorinate, it's not necessary -- for you, in your pool situation -- to specifically work on lowering the alkalinity. Instead, just use muriatic acid to keep the pH in the 7.0 - 7.4 range. If you do so, the alkalinity will drift down over time, all by itself UNLESS you cover it with a gas tight membrane, like a solar cover.

The high alkalinity is only a problem for you if you add some sort of calcium OR raise the pH suddenly. Do NOT use baking soda (Alkalinity Increaser), soda ash (pH UP) or calcium chloride (Calcium UP) in your pool. If you happen to overdose with muriatic acid, let some kids splash around . . . and the pH will rise, along with the drop in alkalinity. If for some reason you do need to raise the pH use ONLY borax.