Just because water comes from a well doesn't automatically mean it's going to have a high calc level. Also, I'm curious how dosing with manganese (Epsom salts) is going to help a calc problem.
Lime is calcareous, as is aragonite, dolomite, and crushed coral (all used for aquaria). You could try compounds made for African cichlids to bring up the calc levels and that would also raise the alkalinity (buffering capacity) of your water. I am a big fan of SeaChem's product lines for this, again, specifically in aquaria.
There is a way to treat the water so it doesn't "lock" as you say, but honestly I am not very familiar with how that works and haven't yet been able to wrap my head around water with high calc content that isn't also strongly buffered.