The amount of salt used per regen will dictate the amount of capacity you will achieve. In other words, using 15 lbs of salt on a 1 cf unit will yeild 30k grain. That same cf unit using only 6 lbs of salt, will yeild 20k grains. As you can see, with the lower salt setting is more effiecent than the higher amount. Using this formula, you can set any size unit. 1 gallon of water will dissolve 3 lbs of salt. So if you are going to use 9 lbs of salt you need 3 gallons of water. All softeners have a brine flow control. A BFC of .5 will require 6 minutes of fill time (6*.5) to achieve 3 gallons of water. So in your case you need to know the size of the unit (amount of resin) and the BFC size to determine the refill time.