How to Correct Marine Aquarium Salinity

In a marine aquarium, salinity refers to the amount of dissolved salts in parts per thousand (ppt). Specific gravity also measures salinity and expresses the density of the aquarium water compared to the density of water. The specific gravity of water is 1 and anything heavier than water has a specific gravity that is above 1. The ocean has a salinity of between 34 to 37 ppt. At 35 ppt, seawater has a specific gravity of 1.026. Aim to maintain a specific gravity of between 1.020 to 1.026 in your marine aquarium.

Things You'll Need

  • Hydrometer
  • Tap water
  • Container
  • Aquarium water conditioner
  • Synthetic seawater salts
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Instructions

  1. Measure Salinity

    • 1

      Turn off the filters and aeration devices to keep the water calm during testing.

    • 2

      Use a hydrometer to determine the salinity of your marine aquarium. If you are using a rectangular plastic container hydrometer, fill it with some aquarium water. If you are using a cylindrical plastic container hydrometer, place it in the aquarium until it fills up. If you are using a free-floating hydrometer, place it on the water surface.

    • 3

      Read the hydrometer scale when the pointer stops moving.

    • 4

      Turn on the filer and aeration devices.

    Decrease Salinity

    • 5

      Fill an open container with tap water.

    • 6

      Add aquarium water conditioner to neutralize any remaining chlorine. Follow the instructions on the product label. Otherwise, simply leave the tap water out for at least 24 hours to let the chlorine diffuse out of the water.

    • 7

      Add the neutralized tap water to the marine aquarium. Wait for a few minutes and check the salinity again. Add more tap water if the salinity is still too low.

    Increase Salinity

    • 8

      Pour tap water into a container.

    • 9

      Add synthetic seawater salts to the tap water and mix until it fully dissolves. Follow the instructions on the product label. This mix is healthier than seawater because it contains no pollutants or harmful microorganisms.

    • 10

      Pour the synthetic seawater into the marine aquarium. Let it mix for a few minutes and check the salinity of the water again using the hydrometer. Add more synthetic seawater if the salinity remains too low.