We are in a new house, never have used a softener before, and are wondering when to put more salt into the water softener basin. I opened it tonight and it is about half full with salt with a brine up to the level of the salt. When do we need to refill it, when it’s completely empty? Do we just fill this with the big bags of salt from the hardware store or do we need something else? How long does it usually take for the basin to get emptied after filling?