Canuck,
Neither pH Minus nor muriatic acid will lower you alkalinity permanently. Those products are used to lower you pH. To lower alkalinity you'll have the follow the procedures outline here: http://www.poolforum.com/pf2/showthread.php?t=191.

If you're not have trouble controlling your pH (unlikely, it will probably tend to rise with your high alk and the SWG) and you're not getting calcium build up (scale) on anything, you might be able to live with your alkalinity as it is.

Best of luck.