I also have a well and have struggled with harsh aftertaste for a long time (both extract and all grain). Although I am in a different part of the country, moderate to high carbonates seem fairly common in many places, so it is possibly an issue for you as well. Two things that made the biggest difference for me were 1) filtering all my water with a reverse osmosis filter to remove almost all minerals. For all grain I add back Ca via calcium chloride and gypsum. And 2) using hop sacks with pellet hops to reduce the amount of hop material getting into the fermenter. I suspect the water was the biggest improvement even though my carbonates were not super high (total alkalinity 57 ppm CaCO3). These two things helped both my ligheter beers (Kolsh, APA, blonde) and even dark beers (stouts and porters). I also recommend reading the brewing water primer. That helped me alot. This assumes that you pitch plenty of healthy yeast, aerate well and control fermentation temperature. Hope this helps.