The problem with water softeners is that they exchange sodium for the
magnesium and calcium in the water. Remember that hardness refers only
to calcium and magnesium, not total dissolved solids. Thus even though
a water softener reduces the levels of Ca and Mg, it actually
increases TDS, since you get two Na+ ions for each Ca++ or Mg++ ion
removed.

I believe you may be mistaken on this point about a raise in TDS, or for
that matter the two for one exchange of Sodium with either Calcium or
Magnesium. I see little to no conductivity change in softened water and
have read many times that TDS is unaffected using these units. Whats
your source for this information?


It's possible the plants are suffering because the TDS level is too
high, or they have sodium poisoning. (You know how very little lives
in salty soil? Same idea.) Even more likely is that they're simply
starved for Ca and Mg. Adding a fertilizer with these might fix the
problem.

- Jim

In a properly working water softener, the Chloride is not introduced
into the water. One could use Potassium Chloride instead of Sodium
Chloride in the water softener and eliminate the Sodium. I no longer
need to dose Potassium in my tap water tanks, and for my RO water
sourced tanks, I use some pellets from my water softener for the dosing.
I had thought that Chloride was also a bad thing for plants. High
Sodium levels does seem to not be great for some plants.