A sample of seawater from most locations with a chlorinity of 19.37ppt will have a Knudsen salinity of 35.00ppt, a PSS-78 practical salinity of about 35.0, and a TEOS-10 absolute salinity of about 35.2g/kg. The electrical conductivity of this water at a temperature of 15°C is 42.9 mS/cm. [6] [12] Unlike pH meters, salinity meters don’t require frequent calibration. Depending on use, calibration of a salinity meter can be done once every three or four months or manufacturer's on how to care for one. If your probe is continuously submerged in your filter sump, it’s especially important to make sure the probe tip is not covered with slime, algae or other debris. The two electrodes are fairly rugged. You can wipe down the outside of the probe body with a soft cloth and RO water. If the electrodes look dirty, gently remove debris with a soft brush and RO water. Zhang, X.; Peng, W. Temperature-independent fiber salinity sensor based on Fabry-Perot interference. Opt. Express 2015, 23, 10353–10358. [ Google Scholar] [ CrossRef] [ PubMed]

Seawater typically has a mass salinity of around 35 g/kg, although lower values are typical near coasts where rivers enter the ocean. Rivers and lakes can have a wide range of salinities, from less than 0.01 g/kg [3] to a few g/kg, although there are many places where higher salinities are found. The Dead Sea has a salinity of more than 200 g/kg. [4] Precipitation typically has a TDS of 20 mg/kg or less. [5] a b Wetzel, R. G. (2001). Limnology: Lake and River Ecosystems, 3rd ed. Academic Press. ISBN 978-0-12-744760-5.

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If using a glass hydrometer, the measurement will be where the surface of the water touches the meter – make sure you measure the flat water surface, not the meniscus.

Ashokan, R.R.; Thomas, K.; Natarajan, V. Design, fabrication and evaluation of zero external field conductivity cell for CTD sensor. In Proceedings of the 2009 International Symposium on Ocean Electronics (SYMPOL 2009), Cochin, India, 18–20 November 2009; pp. 128–132. [ Google Scholar] [ CrossRef] For practical reasons salinity is usually related to the sum of masses of a subset of these dissolved chemical constituents (so-called solution salinity), rather than to the unknown mass of salts that gave rise to this composition (an exception is when artificial seawater is created). For many purposes this sum can be limited to a set of eight major ions in natural waters, [7] [8] although for seawater at highest precision an additional seven minor ions are also included. [6] The major ions dominate the inorganic composition of most (but by no means all) natural waters. Exceptions include some pit lakes and waters from some hydrothermal springs.Zaky, Z.A.; Aly, A.H. Highly Sensitive Salinity and Temperature Sensor Using Tamm Resonance. Plasmonics 2021, 16, 2315–2325. [ Google Scholar] [ CrossRef]