Hi,
a TDS meter is an electronic test equipment measuring water conductivity. TDS - Total Dissolved Solids. The standard calibration is in uS micro Siemens.
Conductivity in Siemens, 1 S = 1 / 1 Ohm
Resistance in Ohm, 1 Ohm = 1 / 1 S
Dissolved elements increase water conductivity. TDS meter detects how much is present.
Examples:
0.1 uS demineralized DI Kati and Ani Ion-Exchanger
1.0 uS distilled water
10 uS quality RO
30 uS cheap RO
300 uS tap 6 dGH (vary on location)
1000 uS water 16 dGH
TDS meter is for people who are dealing with RO and soft water aquariums. It is a nice tool for RO water preparation and aquarium water maintenance.
Edward