Thank you Gary, that is a very good explanation of capacity vs actual usage. Also thank you for keeping your web site up, it is extremely helpful and useful for newbies, it helped me greatly with the size selection of my softener and helped me avoid costly mistakes!
I've read all of what has been said here about regenerating resin except for the resin manufactures saying it was OK to go 30 days or even 6 months between regenerations as has been claimed here.
Fact, all city water and private well water has turbidity in it; some city waters have more than private wells, mostly due to the condition and type of their water distribution lines and their age.
Turbidity ( and bacteria etc.) buildup in a softener causes a loss of capacity and can cause a resin replacement long before it would have to be replaced if it had been regenerated more frequently. Like every 7-9 days. Kinda like an engine lasting longer the more frequently the oil is changed.
To help you understand the operation of your softener. Compare it to you going to fill up the fuel tank in your vehicle.
Then you drive X miles or X number of days and refill the fuel tank again. It is a 20 gallon tank, it takes 12 gallons to refill it the first time. You can calculate fuel mileage by dividing the miles driven by the gallons needed to refill the tank.
What happened to the other 8 gallons that were still in the tank when you refilled? .... your new softener starts out with 2.0 cuft of fully regenerated new resin = 64K of capacity... You use 13k in say 8 days and have the equivalent of another full day's reserve plus the balance of 64 - 13 = 51K. How many K do you have to regenerate to get full capacity, full capacity will be 60k?
The max is 60k and that is due to the resin being used and you'll not be able to regenerate it to 64k unless you use more than 15 lbs of salt/cuft, and even then it is questionable.
Now 60k takes 30 lbs of salt per regeneration. Looking at salt efficiency you calculate it the same as fuel mileage, 60,000/30= 2000 grains per lb of salt used but... if you only used 13,000 and want a salt efficiency of say 3333 grains per lb, you use 3.9 lbs (round to 4 lbs) per regeneration, that is not per cuft. AND the remaining 60,000 - 13,000 = 47,000 (or 47k), is still in the tank. The same as the 8 gallons of fuel in is your vehicle.
You program the K of capacity for say an 8 day service run plus the reserve and then the salt dose that is required to regenerate that K of capacity and set the calendar override for day 8 or a couple days longer.
The WQA says that a softener is working just fine as long as there is no more than 1 gpg (17.1 ppm or mg/l) of hardness in the softened water. I have sold softeners programed this way for many years without customer complaints or problems.
More frequent regeneration prevents resin problems in the future.