Looking to replace a water softener, please verify my thinking

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Madison, WI
I'd like to buy a new, more efficient water softener. Our current one is about 15 years old and uses about 50 lbs of salt a month - which frankly doesn't sound too bad compared to others. Four people live in our home and our water hardness is 20gpg. We're on city water. Located in Madison, WI if it makes a difference.

4 people x 75 gallons x 20gpg = 6000 grains / day

48,000 grain capacity - 1.5 ft3 resin. BUT perhaps I'd get better salt efficiency out of one size larger, 64,000 grains / 2.0 ft3 resin

I've noticed that Pentair is highly valued here so this might be a good purchase - https://www.homedepot.com/p/PENTAIR-Water-Softener-System-for-5-to-6-Bathrooms-35922/325387647 but its not lost on me that its nearly a grand more than https://www.homedepot.com/p/AQUASUR...tal-Metered-Water-Softener-AS-HS64D/311245270 - Why spend the extra money? I can if there's value, I just want to understand it. The cost of sizing up seems to be negligible, there's a difference in brands / equipment. Perhaps there's better places to buy as well.

Anyway, I hope I've learned something from the forums threads and will be corrected if I've misunderstood anything.
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Your new softener will need 10% crosslinked resin.

I don't recognize that valve in the HD page. "The single rotary disc seal " does not ring a bell.

The Pentair Fleck 5800SXT would probably be good for the valve part.

Two cubic ft of resin is the minimum size I would go with. My calculations are different from yours, including that you don't want to get 64000 grains of softening out of 2 cuft of resin; that would be inefficient. But I also assume 60 gallons per day per person, rather than 75.

One more thing; if that 20 gpm is the "average hardness" number from the water department, you would probably need to account for more. Chances are they mix river (low hardness) with well (high hardness) water, and the mix will vary with how high the river is. It might also vary according to what neighborhood you are in, if there is more than one water treatment plant. The Hach 5-B test is good for measuring your raw water hardness, as well as checking the residual hardness.
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