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Water Care


December 13, 2018 | By Tom Sarac

by Tom Sarac


Electrical conductivity (EC) is a measure of the water’s ability to ‘carry’ an electrical current and indirectly, a measure of dissolved solids or ions in the water. Pure water has a very low conductivity value (nearly zero), hence, the more dissolved solids and ions occurring in the water, the more electrical current the water is able to conduct.


The Fluval G instrumentation senses water through a special conductivity probe consisting of two titanium alloy terminals, which will not age or degrade through oxidation and ageing. The conductivity probe in conjunction with the temperature sensor measures the electrical resistance of aquarium water. The sophisticated software then interprets the electrical signal to calculate and display the conductivity value. The system recognizes if the aquarium contains fresh water or salt water, and automatically displays the correct value in either (micro siemens) µS/cm for fresh water or (milli siemens) mS/cm for marine tanks).

Conductivity meters are available from specialist aquatic stores and online. When buying, be sure that the meter compensates for water temperature, which has a direct effect on conductivity. You should also be aware that most meters require calibration to remain accurate. This needs to be done using water of a known conductivity level, which you will need to obtain separately.


The Fluval G-series filter is the world’s first filter to include an integrated conductivity meter. It is temperate compensated and never requires calibration.

Conductivity level is constantly monitored and is graphed over time on the filter’s LCD screen recording the historical daily readings (1 reading every 12 hours), covering up to 48 days of historical data. You could also set an alarm to show the maximum and minimum settings.

Material of the Electrodes: TITANIUM
Measurement range in fresh water(µS/cm): FROM 10 TO 2000
Instrument accuracy in fresh water from 100 to 1500 µS/cm (%): +/- 5%
Measurement range in salt water (mS/cm): FROM 20 TO 80
Instrument accuracy in salt water from 40 to 80 µS/cm (%): +/- 8%

Note: For a correct reading of the conductivity value at the filter’s first startup or after maintenance operations, it is recommend letting the unit operate for at least 24 hours so any air bubbles trapped in the filter can be released. Otherwise, the probe’s accuracy will be reduced.

It’s also important to note that conductivity is a gross measurement only, and cannot specifically indicate the concentration or presence of any one specific component. The EC Monitoring system is also used to protect the aquarium against other abnormal operation conditions, such as the absence of water within the filter.


To create perfect conditions you need the ability to alter your aquarium’s conductivity level. Fortunately, this is very simple.

To raise conductivity, carefully add dissolved aquarium salt to the aquarium water.

To lower conductivity, perform a partial water change, replacing the water removed with R/O (Reverse Osmosis) water (available from most aquatic stores.) R/O water usually has a conductivity of around 20-30 µs.

Any large water changes should be performed in stages over the course of several days to minimize the effect on beneficial bacteria.


One of the most important issues for aquarium keepers is providing and maintaining a suitable and stable environment for living organisms. EC plays an important role in monitoring both fresh and saltwater tanks, providing a general, but fundamental alert that something is changing inside the aquarium.

It is something similar to the body temperature of a person: a deviation from the ‘normal’ range does not point to a specific illness, but suggests that something is changing or has been altered, and needs to be investigated.

In nature, every biotope can be identified by a complex list of interrelated characteristics. In aquatic environments, EC is a very important element. Fish are very sensitive to this value since conductivity is strictly related to the amount of osmotic pressure exerted on their cellular membranes. While they are well adapted to the specific conductivity range of the environment in which they live, you still have to ensure the fish you are placing into your aquarium are suitable to the water. If the water is not the right environment for them, your fish will need to continuously pump water in or out, so that the osmotic pressure is equalized across their cell membranes.

More and more hobbyists constantly check the conductivity values of their aquariums as a way to understand at a first glimpse what is changing, and then start a deeper analysis of the situation using water analysis test kits.


The following two examples can clarify the importance of monitoring EC in freshwater tanks:

  • In a newly established aquarium, the ionic composition of water can vary considerably during the first few weeks or months. Some types of gravel can trigger ‘ion exchange’ activity or could either release or trap some ions in water. This could dramatically affect the EC value and the aquarist should evaluate which other parameters are involved (GH and KH in this case), by means of some simple water tests.
  • Established aquariums produce wastes that directly or as a consequence of bacteria generate charged molecules that result in an increase of the EC. This slow but constant EC increase suggests that something is changing in the water; again, by using the proper test kits, it is possible to evaluate which parameter is going out of control. For example, the continuous production of nitrates operated by nitrifying bacteria will result in a correspondent continuous increase of the EC value.

The above mentioned examples clearly indicate how important the EC value is. However, at the same time it cannot be used to directly state the origin of a specific problem, but it is rather a general ‘alert’ signal, which needs interpretation by performing further investigations.


In marine aquariums, salinity is the most important parameter to measure and maintain. This can be a challenge since there is a narrow range. There are different methods available for measuring salinity, such as specific gravity, refractive index and also conductivity. However, the latter is recognized by scientists as being the most accurate. Your EC Monitor is an easy-to-use, comfortable and reliable way to keep the salinity of your marine aquarium under control.

Conductivity can be a complex subject and we’ve only scratched the surface but the basics we have discussed, combined with an effective conductivity meter, can revolutionize the way you maintain your aquarium and care for your fish.



Aquatic expert Tom Sarac provides an in depth look at the Hydrotech performance monitor from the revolutionary Fluval G-Series aquarium filter.


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