Salt Content/Salinity

The salt content, also known as salinity, describes the amount of salts dissolved in a liquid. In natural waters, the largest proportion of these salts usually consists of sodium chloride (common salt), but other minerals and ions are also present.

Salinity is an important parameter for water quality and influences numerous biological and chemical processes. Regular monitoring of salinity plays a particularly important role in seawater aquariums, aquaculture, environmental monitoring and industrial applications.

Typical units for specifying the salt content are percent (%), parts per thousand (ppt) and PSU (Practical Salinity Units).

salinity aquarium anemone stockphoto
To all products

Why is it important to measure the salt content?

Salinity has a direct influence on organisms, chemical balances and the properties of a solution. Even small changes can have an impact on the stability of an ecosystem or the quality of a process.

Salinity measurement is used, among other things, for

  • Sea water aquaristics
  • Aquaculture and fish farming
  • Environmental monitoring
  • Coastal and marine research
  • Water treatment
  • Industrial processes
  • Laboratory applications

Regular monitoring helps to detect changes at an early stage and ensure optimum conditions.

How is the salt content measured?

Modern salinity measuring devices generally determine the salinity via the electrical conductivity of a liquid. As dissolved salts influence the flow of current, the conductivity increases with increasing salinity.

Our salinity measuring devices use the Practical Salinity Scale (PSS-78), an internationally recognized method for determining salinity. The corresponding salinity is calculated from the measured conductivity.

Depending on the device, the measurement results can be displayed in PSU, ppt or percent. The automatic temperature compensation ensures reliable and reproducible measurement results even with changing temperatures.

What factors influence salinity?

The salt content of a liquid can be changed by various natural and technical influences.

These include, among others:

  • Evaporation
  • Precipitation
  • Freshwater input
  • Water change
  • Industrial processes
  • Dissolved minerals and salts

Continuous monitoring enables such changes to be detected at an early stage.

Salinity, conductivity and TDS: What’s the difference?

Salinity, conductivity and TDS are closely related, but describe different properties of a liquid.

The salt content indicates the concentration of dissolved salts. Conductivity describes the ability of a liquid to conduct electricity. The TDS value (Total Dissolved Solids), on the other hand, represents the estimated total amount of all dissolved substances in the water.

As these parameters are interlinked, many modern measuring devices can record and display several values simultaneously.

Salinity meters from Apera Instruments

Apera Instruments offers precise measuring instruments for the determination of salinity for applications in aquaristics, aquaculture, environmental analysis, research and industry.

Thanks to modern sensor technology, automatic temperature compensation and simple operation, our devices enable fast and reliable measurements directly on site or in the laboratory.

Frequently Asked Questions

What is a normal salinity level in the ocean?

The average salinity of the world’s oceans is about 35 ppt (parts per thousand) or 35 grams of salt per liter of water. The North Sea, at about 30–34 ppt, is slightly below this, while the Baltic Sea, at 5–15 ppt, is significantly lower. The Red Sea and the Persian Gulf reach up to 43 ppt due to high evaporation rates.

What is the ideal salinity level for a saltwater aquarium?

For saltwater aquariums with corals and marine fish, a salinity of 33 to 35 ppt is recommended, which corresponds to a specific gravity of 1.023 to 1.025. Regular measurements are important because evaporation increases the salinity, which must be compensated for by adding freshwater.

What is the difference between salinity, conductivity, and TDS?

Conductivity (EC) is the electrical parameter measured directly in µS/cm or mS/cm. TDS and salinity are calculated from this value. TDS indicates the total amount of all dissolved solids, while salinity specifically describes the concentration of dissolved salts—expressed in ppt or parts per thousand.

What salinity level is important for aquaculture and fish farming?

In aquaculture, the optimal salinity varies greatly depending on the fish species. Euryhaline species such as salmon tolerate wide fluctuations (0–35 ppt), while stenohaline marine fish require a constant salinity of 30–35 ppt. Precise and regular monitoring is crucial for the growth and health of the fish.

How accurately do Pocket Testers measure salinity?

Apera salinity meters, such as the Salt20, measure in the range of 0 to 10.0 ppt with an accuracy of ±1% of the full-scale value. Regular calibration using the supplied calibration solution is necessary to ensure precise results. Meters such as the EC60 or PC60 measure salinity in addition to EC, TDS, and other parameters.

To all products