You mix the salt and water a day before the change and let it sit with a powerhead for circulation and a heater for the temperature. Then you add it to your tank. Never add salt directly to your tank.
I also have well water.You could buy bottled water or in my case I have a 125 which is a lot of water,get a Pik or Britta filter for your sink.Thats what I have.How hard is your water?