[QUOTE="Reach4 ...it is possible that the small softener uses a salt-inefficient 15 lb/cuft of salt for regen getting 30000 grains . You will probably use 8 lb per cubic ft (getting 72000) to 6 lb/cuft (getting 63000 grains of softening)...
Each night at about 2AM, the softener checks to see if it has enough remaining capacity to make it through the next day. If it has enough to meet the reserve, it waits. If not enough, it regens. So you might average leaving around 1/2 day of salt unused... If you are regenerating every 3 days, 1/2 day is significant. If regenerating about every 7 days, less significant.[/QUOTE]
I'm finally understanding the importance of that. I have that chart and am shooting for the 8lb range.
[QUOTE="Bannerman ... A softener containing 1 ft3 resin is normally installed in a 9" X 48" tank. As your tank is only 35" tall, it is likely it contains only 3/4 ft3.... Further to what Ditttohead has said about the efficiency of a specialized resin, almost all softeners may be programmed for higher efficiency depending on the Capacity setting. For instance, a 1 ft3 unit programmed to regenerate when all 32,000 grains resin capacity has been depleted, will require 20 lbs salt each cycle to regenerate that capacity... [/QUOTE]
All that sounds spot on. Just by eyeball on the salt level (cabinet type tank), I'd guess 1/3 up to ½ of a 40lb bag per regen.