Ah, the engineer in you wants to know. Then Mr. Engineer you know that to measure something you need the correct measuring device. You wouldn't use a dual trace O-scope to measure atmospheric pressure would you?

TDS is no measure of water hardness. TDS will vary depending on water conditions including hardness. Your TDS meter is invaluable in testing the performance of a reverse osmosis unit.

Google water hardness test and you'll get about 1,180,000 results. You want hardness test strips or a hardness test kit to measure hardness. Simple hardness test strips will do the job and are cheap. You might try a local aquarium store for test strips.

If your softener was sized correctly for your water conditions and water usage and if it was installed correctly and if it was set up correctly for efficiency then your treated water should measure 0 hardness.

If it doesn't test 0 hardness then you've got some work to do.

All the softener techs in my area use the test kit linked below. Cheaper kits/strips available at local hardware stores but I test regularly and thought this kit worth the extra for my two monitored locations.

My TDS is the same out of the softener as it is inbound. TDS is not a measure of "softness", although zero TDS certainly would be soft.

Here is a link that might be useful: Hardness test kit that I use

Thx for the reco on the Hach test kit. I've seen that particular kit recommended in other water forums. I'll get one and see what it says.

For the most compreshensive test of your water treatment system take a sample of the raw water before it enters the treatment system and a second sample of water that has passed through the treatment system and send both samples to a lab that will do a complete water analisys then compare the results.

Results from the Hach test: supply water, 9 drops/GPG; softened water immediately turned blue with 1 drop. The water lab test I had done prior to installing the softener listed water harness, CACO3, at 180ppm which would seem to be consistent with the 9GPG.

And now you know.