? Efficacy of Using TDS to Calculate Softener Refill Time ?

You guys set me straight with regard to TDS being useless in checking water softener output (since the TDS reading of the softened water might even exceed that of the incoming hard water)...many thanks for that little piece of enlightenment (I got the great Hach 5 kit for that test, as you suggested, and really love it!).

However, my research seems to be suggesting that, for all practical purposes, the TDS in source water can be used to calculate a softener's salt dosage requirement. How does that approach sit with you guys? And, if that isn't practical, what's the best approach to determining refill time on my Culligan Soft-Minder Twin Model 9100?

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.