To "soften" water is to remove calcium (among other things like iron) from the water and that is commonly done by one of two methods.
One method is ion exchange as done by a water softener. A water softener exchanges either sodium ions (if using NaCl) or potassium ions (if using KCl as a SALT SUBSTITUTE) for calcium (and other) ions in the hard water. That's it, no ifs, no ands, no buts, and no sales double talk. Simple chemistry and physics. Softening water is not black magic. It is physics and chemistry with a side of mechanics. No matter how hard sales people try (and want) to they can not violate the laws of physics or change the nature of chemical actions and reactions.
The other is by a filter, but no simple filter will remove calcium. You would need a reverse osmosis unit large enough to service your entire house. You would not want to pay for that big an RO nor pay for the service and routine maintainence it would require and RO water would be very agressive in your plumbing and it would waste a lot of water.
NO magnet(ic) gizmo or electronic gizmo or "conditioner" or carbon filter will soften water but people waste their money on them EVERYDAY.
Check out this URL for one story
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and there are many more on the net if you Google.
Pick the right softener (not a box store brand), size it properly for your water conditions and usage and the SFR of your plumbing, and get a competent install and you should go 15-20 years.
The MOST IMPORTANT thing is that water treatment begins with a complete water test so you know what needs to be treated or filtered out to get the quality water you want.
If you want to know more about that "slimy feeling" that comes with soft water go here...
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