Use a **total water hardness test kit**. Test strips give a quick reading; a drop-count titration kit gives a numerical result by counting drops until the sample changes colour. Choose one that measures both calcium and magnesium. [Hach’s hardness testing guide](https://www.hach.com/parameters/hardness) explains the method.

To check your softener:

1. Test cold water from a point **before the softener**, such as an outdoor tap you know receives untreated water.
2. Test cold water from a tap **supplied by the softener**. Run it long enough to flush water sitting in the pipe.
3. Compare the readings. A working salt-based softener should produce very low hardness. Similar readings suggest it is bypassed or needs attention.
4. Repeat after a regeneration cycle. If hardness falls and then returns before the next cycle, check the capacity and regeneration settings.

Kits usually report hardness as **ppm or mg/L as calcium carbonate**, or **grains per gallon (gpg)**. One gpg equals approximately 17.1 mg/L. [Hach](https://sk.hach.com/product.detail-print.version.jsa?id=25116425015)

For context, the [USGS hardness ranges](https://www.usgs.gov/water-science-school/science/hardness-water) are:

| Hardness, mg/L as CaCO₃ | Classification |
|---:|---|
| 0–60 | Soft |
| 61–120 | Moderately hard |
| 121–180 | Hard |
| Over 180 | Very hard |

An electronic **TDS meter does not measure hardness**: it measures dissolved substances collectively. Use a hardness-specific test to assess the softener.