How to Adjust Aquarium Salinity

Maintain proper salinity in your aquarium to keep your fish healthy.
Maintain proper salinity in your aquarium to keep your fish healthy. (Image: Jupiterimages/ Images)

Maintaining proper salinity in your saltwater aquarium is essential for the health of your fish. Since most saltwater fish contain more salt in their bodies than the water surrounding them, they transfer water from their bodies to their environment through osmosis. If the salt content of the water is too high, reverse osmosis happens and your fish will dry out because the water will transfer from an area of high concentration (inside the fish) to low concentration (the water). Measure your aquarium's salinity regularly and balance the levels out by adding salt or water.

Things You'll Need

  • Hydrometer
  • Salt
  • Dechlorinated water

Measure the salinity of your aquarium using a hydrometer. Hold the handle of the hydrometer and slowly dip the mouth of the container into the center of the aquarium. Once full, remove it and place it on a flat surface. If you see any air bubbles, tap the side of the container to release them. Note the hydrometer's reading. Find out what temperature your hydrometer is calibrated to work at and make the necessary conversion according to the operating manual's conversion table. The normal range is 1.012 to 1.024. If it reads below that, you need to add salt. If it reads above that, you need to dilute the water.

Add a little bit of table salt to your aquarium if the salinity level is low. Remeasure the salinity level using the hydrometer. Add more table salt if necessary.

Add dechlorinated water to your aquarium if your salinity level is too high. Remeasure the salinity level using the hydrometer. Add more water if necessary.

Tips & Warnings

  • Evaporation of water is the primary reason for high salinity levels. Monitor your salinity levels regularly and remember to keep your aquarium water levels consistent.
  • DO NOT raise or lower you salinity more than 2 degrees in any 24 hour period. If you must change it more, you must do a series of water changes, each at least 24 hours apart.
  • DO NOT change more than 50% water in your aquarium at one time
  • DO NOT use salt water to top off your aquarium because salt does not evaporate!

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