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What is Electrical Conductivity?

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.

How does the Fluval G EC Monitoring System measure the Electrical Conductivity in my aquarium?

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).

The system constantly monitors aquarium conductivity and also provides a rolling line graph, which records the historical daily readings (1 reading every 12 hours), covering up to 48 days of historical data. You also have the ability to set an alarm to show the maximum and minimum settings.

Type Contact type,
Contact type,
Material of the electrodes TitaniumTitanium
Measurement range in fresh waterµS/cmfrom 10 to 2000from 10 to 2000
Instrument accuracy in fresh water from 100 to 1500µS/cm %+/- 5%+/- 5%
Measurement range in salt watermS/cmfrom 20 to 80from 20 to 80
Instrument accuracy in salt water from 40 to 80µS/cm %+/- 8%+/- 8%
Note: For a correct reading of the conductivity value at the filter's 1st 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 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.

Why is Electrical Conductivity so important in aquaria?

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.

EC in Freshwater

A couple of examples can clarify the importance of monitoring EC in fresh water 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 the following example (see graph below), the EC value of a 300 liter aquarium has shown an increase of 30% in 37 days. After performing some chemical analysis, it was possible to see that at least a part of this increase was due to Nitrates, which in the same period have risen from 23 to 40 mg/L as NO3-.
By simply making a 30% water change (using osmotic water), we were able to re-establish the original values to around 250µS/cm.

EC value of a 300 liter aquarium has shown an increase of 30% in 37 days

EC in Saltwater

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.

How can I monitor my aquarium using the Fluval G Filter's EC Monitor?

Fluval's G Filer Monitoring System has been designed to help you easily monitor the EC values. You will find that as you become more comfortable with the system, maintaining your EC levels will become quicker and more accurate.


When starting a new fresh water aquarium and before introducing fish, it is good practice to measure the water hardness value (GH) and evaluate if this value is suitable for the fish you are about to introduce. In other words, by knowing the GH value of our aquarium water, you can determine which species of fish will thrive in that type of water.

In a newly established aquarium, conductivity will be roughly related to General Hardness (GH= sum of divalent ions, mainly Calcium and Magnesium) and TDS (Total Dissolved Solids) values: µS/cm x 0.5 = ppm TDS x 0.056 = dGH.

Therefore, when buying a freshwater fish, it is very important to know the EC value the fish was living in, and which level will be needed to keep the fish healthy.

For community freshwater tanks, the EC value may generally range from 100 to 300 µS/cm; Discus, Paracheirodon and other soft-water species require values below 100, while Cichlids from African lakes (Malawi e Tanganyika) thrive at values above 500 µS/cm.

Once the most suitable conductivity range for your marine life has been determined, the best use of the conductivity meter in your filter is to monitor the changes in water conditions. Unwanted inorganic and organic pollutants, as well as fertilizers and other chemicals added to the water by the aquarium keeper, directly affect the EC value, generally by increasing it.

In fact, every chemical, additive, piece of food, medication or conditioner you put into your tank affects the conductivity in your aquarium and the above mentioned "link" becomes less. Therefore, measuring conductivity is a way to continuously monitor the conditions of water, since a change in conductivity also indicates a change in water conditions. Any of these changes should be checked using a chemical analysis (test kit). Sometimes the easiest way to correct the EC value is to change the water, thereby reducing the concentration of pollutants.

When starting up a new aquarium, get your water ready before you introduce the new species. Plan for a few days for the water to reach a constant temperature and the correct EC readings to be established. If the filter monitor is showing an EC value that is too high, the solution is to dilute the water with an appropriate amount of de-ionized (osmotic) water (a simple formula to calculate how to dilute water is: litres of water needed / actual dGH value x desired dGH value).
E.g.: if your 80 liter tank has a GH value of 20 dGH and you want to reduce this value to 5 dGH the calculation is: 80 / 20 x 5 = 20 (liters of actual water) + 60 (de-ionized water) = 80 liters of 5 dGH water.
Or, in other words, you need to replace 60 liters of your tank water with de-ionized water.

On the contrary, if the filter monitor shows that the EC value is too low for the species (for example you want to put African cichlids in your aquarium) then you need to "harden" your water. This can be done by using some commercial salt mixes or solutions i.e calcium carbonate.


Here salinity is the parameter to use in order to control the conductivity measurement. Other than organisms coming from particular environments and requiring specific salinity levels, salinity should generally average at a conductivity value of 53 mS/cm (= 35 PSU or ppt = 1.0285 specific gravity). The following comparative table can help if you are more used to salinity or specific gravity than to EC (values at 25°C; highlighted values are those typical of ocean waters):

To obtain the correct salinity level for your aquarium, simply fill the tank with de-ionized (osmotic) water. Turn on the heater and wait until the water has reached the desired temperature. Then, assuring an adequate water movement, slowly add the salt until the EC reading reaches the value of 53 mS/cm. Please note that the complete dissolution of salt, and therefore the correct EC reading, needs at least 24/48 hours.

mS/cmSalinity (PSU)Specific gravity

Does my EC Monitor require any maintenance?

The EC monitoring system does not require maintenance. It is however recommended to periodically clean the conductivity terminals located on the underside of the filter lid by rinsing with a soft jet of water.

Fluval G Electrical Conductivity (EC) Monitoring System


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