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Water Care


December 13, 2018 | By Tom Sarac

by Tom Sarac


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, pieceof 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. Anticipate a few days’ time 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: litres (or gallons) of water needed divided by actual dGH value multiplied by the desired dGH value.

Example: If your 80 litre tank has a GH value of 20 dGH and you want to reduce this value to 5 dGH, the calculation is: 80 divided by 20 multiplied by 5 = 20 (litres of actual water) + 60 (de-ionized water) = 80 litres of 5 dGH water. Or, in other words, you need to replace 60 litres of your tank water with de-ionized water.

Alternatively, if the filter monitor shows that the EC value is too low for the species (i.e. 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.)

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.


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.



Aquatic expert Tom Sarac provides an overview including key features and benefits of the revolutionary Fluval G-Series aquarium filter.


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