How To Easily Measure The Saltwater Aquarium Salinity

saltwater aquarium salinity

The salt content in the saltwater aquarium is one of the most important water values. You should therefore learn how to read and regulate the salinity in the saltwater aquarium.

In natural sea water, the salt content is around 34.7 to 35 grams per liter. There are various options for measuring the saltwater aquarium salinity as presented below.

What is Saltwater Aquarium Salinity?

Saltwater Aquarium Salinity is the measure of dissolved salt content in the aquarium water. The salinity is measured in parts per thousand (ppt) or specific gravity (sg). The more salt in your water, the higher your readings will be. 

Saltwater aquarium salinity is usually kept between 1.020-1.028sg or a salinity of 35, which is used as a reference value. This means that 1l of seawater contains 35 grams of dissolved salts. Since the salinity is a temperature-independent value, it is the most precise method for measuring the salinity. 

Salinity is what distinguishes sea water from fresh water. This extremely important parameter must be determined as precisely as possible. 

Methods of measuring the saltwater aquarium salinity

1. Salinity in the saltwater aquarium is determined as density

In practice, the determination of the density is the most common method for measuring the salt content in seawater aquariums. 

The disadvantage here, however, is that the density depends on the temperature.

This means that the volume of water decreases as it gets colder and increases in volume as it warms up. 

However, the amount of dissolved salts in the water remains unaffected by changes in temperature.

Therefore you have to measure the water temperature every time you measure the salinity via the density. 

How to measure the saltwater density using hydrometers (spindles)

  • High-quality hydrometers are calibrated to 25 ° C and only show the exact density in this temperature range.
  • Most hydrometers have a measuring range of 1.018 to 1.028
  • For healthy growth of coral is the ideal density from 1.022 to 1.023 at a temperature of 25 ° C

The decisive factor here is not whether the saltwater density is 1.022 or 1.023, but that the value is constant and does not fluctuate.

Fluctuations in the salt content in the saltwater aquarium always lead to stress for fish and corals.

Factors that contribute to the fluctuation in saltwater density are:

  • The evaporated water is not automatically refilled or when the water is changed
  • The added seawater has a different density

Tips for correctly using a hydrometer

  • When measuring density, the mistake is often made that the highest water level is measured on the hydrometer and not the actual water level. The decisive value for the measurement is the actual water level on the hydrometer. This reading error leads to a permanent shift in density.

In addition to spindles, specialist retailers often offer flat plastic containers with a measuring arm for density measurement. Using these measuring arms is at times inaccurate because air bubbles often form on the underside of the measuring arm. 

The associated stronger buoyancy of the measuring arm then indicates a wrong measured value. Even in comparison tests in which this possible source of error was excluded, precision hydrometers provided significantly more accurate measured values.

The best hydrometer to ensure accurate density measures

ATC Salinity Refractometer

saltwater aquarium salinity
ATC Salinity Refractometer
  • It comes with a specific Gravity and PPT scale which lets you read the results in two different units at the same time in just one test.
  • The refractometer is equipped with a automatic temperature compensation function to minimize the impact of temperature on accuracy.
  • It is easy to clean because it comes in a hard case, droppers, a screwdriver, a user manual and a cleaning cloth.

The scale range of this refractometer is 0~100‰ ( 1‰=1 PPT=1000PPM, PPT means” parts per thousand”, PPM means”parts per million”), it also shows the corresponding specific gravity range 1.000 to 1.070. These are the most common units to show salinity of water. With this refractometer you can get the result in two different ways at the same time in just one test.

The min reading resolution is 1 ‰, this makes it possible to measure low concentrated salt solutions.

Get the ATC Salinity Refractometer HERE

2. Conductivity in salt water aquariums

The seawater aquarium salinity can also be determined via the conductance using an electronic measurement. This measurement can be carried out permanently by an electrode for example in the filter basin.

Alternatively, just like the density, the conductance is also temperature-dependent. However, this is irrelevant in day-to-day practice, as high-quality conductivity measuring devices have automatic temperature compensation.

Here, the reference value is always a converted temperature of 25 ° C

How to measure conductivity in a saltwater aquarium

For an exact measurement result, you must regularly clean and calibrate the conductivity probe

The conductance is given in a saltwater aquarium in millisiemens / cm (mS / cm)

The ideal conductance is between 51 and 53 mS / cm

As with the density, a constant value is also required here.

The best saltwater conductivity meter

HoneForest TDS Meter

HoneForest TDS Meter

The HonesFirest TDS Meter is an accurate, reliable and easy to use TDS, EC &Temp water tester reader, with backlit and auto-lock function.

It comes with an advanced digital ppm meter pen with Advanced Microprocessor Technology, combines TDS Meter (Total Dissolved Solids), EC Meter (Electrical Conductivity) and Temperature meter all in one ergonomically designed pen.

Features of the HonesForest TDS Meter:

  • Automatic Temperature Compensation(ATC)
  • Equipped with backlit LCD for easy reading. If TDS≤40, the backlit color is green, If TDS>40, the backlit color is red.
  • Auto-Lock Function: From test beginning, the reading can be stabilized in seconds, and locked automatically for easy read and record.
  • Hold Function: Before reading locked automatically, the reading can be locked manually if press “HOLD”.
  • Factory Calibrated: No need calibration by user.
  • Auto-Off in 2 Minutes to conserve battery.
  • A colorful TDS chart on the back to explains ppm readings.
  • Includes a protective carrying case with belt clip, easy to carry.

Get the HonesForest TDS Meter HERE

Calibrating the salinity in the saltwater aquarium

If the conductivity of the saltwater in the aquarium is too high:

  • Clean the saltwater
  • Calibrate
  • Measure the conductivity again

If the density is different

  • measure the water temperature

How to calibrate the salinity in the saltwater aquarium

  • If the salt content is actually too high, some aquarium water can be sucked off and replaced with fresh water. However, this must be done in small steps and ideally over several days. The salt content must be measured after each step.
  • If the salt content is actually too low, the evaporated water can be replenished with seawater instead of fresh water. However, this must be done in small steps and ideally over several days. The salt content must be measured after each step.

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