First off, great site, and the iPhone App is cool Jason! (when is the Borate calc coming? ) 8-)
So here's the story; our pool is going on three years old. 13' x 28' x ~4.5' infinite edge with a 3.5' x 26' x 2' overflow sump which equates to around 13k gallons total. SWG, Pebble-Tec, Sand...