Measuring Salinity: Values and Measuring Devices

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).

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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.

The most important difference between our salinity meters is their measurement range. Seawater ranges from 33 to 35 ppt, a saltwater pool from 3 to 4 ppt, and brine well above that. The following overview shows which device covers which range.

Measuring range	Device:	Typical Application	Price starting at
0 to 10.0 ppt	Salt20, EC60, EC60-Z, PC60, PC60-Z	Freshwater aquariums, brackish water, saltwater pools, food	83.30 euros
0 to 25.0 ppt	SX650	Brackish water, aquaculture in the lower salinity range	126.14 euros
0 to 100.0 ppt	5052, SX731, SX751	Marine Aquariums, Aquaculture, Marine Research	113.05 euros
0 to 20.0%	5053	Brine, curing brine, industrial processes	113.05 euros

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?

It is not only accuracy that matters, but also the measurement range. The Salt20, EC60, and PC60 measure from 0 to 10.0 ppt with an accuracy of ±1% of the full-scale value, thereby covering freshwater, brackish water, and saltwater pools. This range is not sufficient for seawater with a salinity of 33 to 35 ppt. The 5052 is designed for this purpose, with a range of 0 to 100.0 ppt, while the 5053 is intended for high concentrations, with a range of 0 to 20%. For precise results, regular calibration with the supplied calibration solution is necessary in all cases.

What kind of testing kit do I need for a saltwater aquarium?

A saltwater aquarium typically has a salinity of 33 to 35 ppt. The device must therefore cover this range. The 5052 salinity meter for saltwater is suitable, with a measurement range of 0 to 100.0 ppt, a resolution of 0.01 or 0.1 ppt, and automatic temperature compensation. Unlike with hydrometers and refractometers, there is no need to take a sample: The device is held directly in the tank and provides a stable reading after about 10 seconds. Pocket Testers such as the Salt20 or the EC60 have a maximum reading of 10.0 ppt and are not suitable for saltwater.

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