What Is the Right Salinity for Salt Water Tanks?

Saltwater fish tanks can enthrall and relax with vivid colors and quirky animals. They can also be a lesson in chemistry. The constant measuring and supplementing can be challenging but also rewarding. One of the most important parameters is salinity.
    • Beautiful Saltwater Fish Tanks like this One Require Precise Salinity Measurements

    Salinity

    • According to the Encarta, Salinity is the measurement of dissolved solids in a given amount of water. In sea water, the most common dissolved solid is sodium chloride, or as we call it, salt. Salinity is expressed in parts per thousand or, PPT, in 1000 grams of water. One gram of salt in 1,000 grams of water is equal to 1ppt. According to the Office of Naval Research, the average ocean salinity is 35ppt. Depending on the location the animals you wish to keep come from, the salinity can be very different.

    Fish-Only Tanks

    • A lionfish is a typical inhabitant of a fish only tank

      If you are planning on keeping only saltwater fish in your tank without any coral, a salinity range of 26 to 30 will help reduce the chances of itch in the tank and make it easier for the fish to breathe. According to The Saltwater Manual, fish require less energy to maintain osmotic balance when the salinity is lower.

    Reef Tanks

    • Anemones benefit from a higher salinity

      If your tank contains large amounts of corals and other invertebrates, however, the salinity should be kept higher, around 33 to 37 PPT. Corals need this higher concentration to create their hard bone-like skeleton. They also benefit from the increased amount of trace elements present.

    Brackish Tanks

    • Sea horses are common in brackish seagrass beds

      Brackish waters occur where rivers flow into the ocean. There are often mangroves, sea grass and mud. According to the Office of Naval Research, the salinity of brackish waters is around 16 PPT.

    Considerations

    • For the common aquarium owner, a salinity probe may prove to be too expensive. A more cost-effective method of measuring salinity is with a hydrometer. Hydrometers actually measure specific gravity, the ratio of saltwater to freshwater, but can easily be converted to salinity. In fact, many hydrometers have the salinity measurements next to the specific gravity.

    Warnings

    • Table salt is iodized for human consumption and cannot be used for a marine aquarium. Also, many sea salt manufacturers add other essential metals and supplements your tank would benefit from. So it is best to use salt specifically made for the type of aquarium you wish to keep.
      Before buying a hydrometer, make sure it is made for the temperature your tank is; 60 degrees F will give much different readings than 75 degrees F.