TDS tester (for PPM)

Hi,

I am seeking for a good TDS tester to check the silver concentration (PPM).

At ebay are a number of devices for prices starting around USD 5.00. At least one of them is quoted to "calibrate with NaCl". Calibration is usually a complex process that is hard to trust, specially for home use.

If you are using a TDS meter, can you share what brand/model it is, if requires calibration, kind of battery is used (button like, AAA, ...) and your overall experience?

I will also appreciate if you can recommend some good (and cheap) model.

Sukhoi