baldheadracing wrote:I'd try a different test kit and/or a TDS meter.

A conductivity TDS meter is great for checking an RO system , but is of little use when checking a conventional softener like this which replaces each magnesium or calcium ion with two sodium ions. The conductivity is not reduced, in fact it goes up slightly after softening.

Some people with conventional cation softeners prefer using GH test kits that are designed to measure very low hardness levels, like the Hach HA-71. In this case, where the kit is measuring both tap water and filtered water in the same 100 mg/L ballpark I don't think the more sensitive kit is called for. But I suppose trying another kit may be worthwhile.

I used the test kit on RO water I got from the market. It's registering super low GH so I think the kit is ok.