Install a conductivity probe in your tank/sump to control salinity, not your salt bin. Setup two tops offs, one from fresh water the other from saturated salt solution. Program controller to use fresh water if salinity => traget, and saltwater if < target. Set alarm if salinity drops below a certain point to remind you to refill salt. You can program a pump to remove water from your display on a timer, set top off control to allow extra top off time during this interval.
Something like this which is what I'm implementing, I've done a few similar ones before but you need a controller like profilux.
I never had issues relating to calcium, alkalinity, or other measurable elements as far as I could tell. Auto water changes were kept small and on a daily bases to prevent large swings and they system also had a reactor or dosing system due to high demand.