"Ed Sirett" wrote in message
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The problem is that a water softener is a _huge_ restriction on the
flow
and
with any form of direct HW systems it will be the bottle neck.

Best have a phosphor in-line descaler.

As to whether this is best or not will depend on the reason the OP wishes
to threat the water.
Adding phosphates is not the same as exchanging ions and that's not the
same
as removing ions.

This is a borderline mains pressure system. Anything that may restrict
flow/pressure should be avoided. Most people only want to descale. A
phosphor canister does that well and does not restrict flow.