Proper choice of water softener system using resin bed volume and efficient salt

I have a private well with the following water properties:
26 GPG Hardness
2.5 ppm Iron
0.5 ppm Manganese
This results in a total Hardness of about 40 GPG
4 persons in the household @ 75 g per day per person = 300 gallons per day
300 gpd * 40 gpg = 12000 grains of hardness per...
Proper choice of water softener system using resin bed volume and efficient salt