How to Measure the Salinity of a Freshwater Aquarium

The water in freshwater aquariums has almost no salt content. At times, it becomes necessary to add salt to kill bacteria or because of problems with parasites that cause aquarium fish to lose their scales -- the added salt helps the fish maintain salt in their blood during the healing process. However, as a general rule, salt should never be added to a freshwater aquarium. Freshwater aquariums with a higher than normal salt content should be adjusted through a 30 percent water change -- as opposed to the weekly 15 percent water change -- as soon as possible. A salinity refractometer can tell you exactly how much salt is present in your freshwater tank.

Things You'll Need

  • Salinity refractometer
  • Reverse osmosis (R.O.) water, distilled water or refractometer calibration solution
  • Paper towel
  • Eye dropper
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Instructions

    • 1

      Rinse the salinity refractometer using either reverse osmosis -- R.O. -- water or distilled water. Wipe the outside of the refractometer with a paper towel. Allow the inside of the refractometer to air dry.

    • 2

      Calibrate the refractometer by adding three drops of R.O. water, distilled water or refractometer calibration solution to the inside of the meter using an eyedropper. Look through the refractometer's eyepiece and turn the calibration screw until it reaches "0." Pour off the water from inside the refractometer. Empty the eyedropper as well.

    • 3

      Add two or three drops of freshwater from your aquarium to the refractometer and review the reading through the eyepiece.