Hot!!! HM Digital ZT-2 TDS Water Tester - for colloidal silver ppm testing Best Gift!!! Range: 0 - 999 ppm (mg/L) EC-to-TDS Conversion Factor: NaCl (avg. 0.5) Resolution: 1 ppm (0-999 ppm) Accuracy: +/- 3% Power source: 2 x 1.5V button cell batteries (included) (357A or equivalent)