Deephaven wrote:I have dual softeners to make sure that the flushing is done with softened water. My well is hell however so any leak through would be bad.

That is one advantage to dual tank softeners. The other is that you don't have time periods where the water softener is bypassed. Single tank whole house softeners do their regeneration on a time schedule that flips a softener bypass valve at say 3AM while it does the regeneration and flush. If you use water during that time period you pull unsoftened water into the plumbing lines.

I think the possibility of a chloride spike in the treated water after a regeneration is there for both single and dual tank systems, and just depends on how much water, softened or not, is flushed through the resin after the regeneration brine cycle has finished. It would not be hard to evaluate this if you have relatively chloride-free tap water and a softener system that allows you to manually start a regeneration cycle. (I have neither at my house.) A simple chloride ion drop test kit could measure whether you are getting a chloride spike in the treated water.

One thing to consider: Run an extra 240V line. Who knows when that new euro-only or awesome vintage lever appears that you decide you need to have.