Contents of Brackish Water

Brackish water is midway between freshwater and saltwater. It contains salt and fish are able to adapt to the slightly saline environment, but salt levels are not high enough to sustain deep sea fish. Freshwater fish such as archer fish and mollies can thrive in slightly salty water, but most brackish fish are originally marine-based from areas where fresh inland water mixes with sea water in bays, deltas and swamps.

  1. Salt Content

    • The salt content of brackish water varies in nature, but as a guide, if you are setting up a brackish fish tank, add at least 1 tbsp. of salt per gallon of fresh water. Sea water contains the equivalent of 8 tbsp. of salt, and you can safely add up to 4 tbsp. per gallon to your brackish tank before it becomes too salty. Use synthetic sea salt, designed for marine aquariums, to create a stable brackish environment. Marine salt is manufactured to contain essential minerals required by salt-loving fish and plants. Standard tropical aquarium salt is adequate, but it can lead to fluctuations in pH due to its lack of natural sea minerals.

    Measuring Salinity

    • Measure salinity levels with a hydrometer to find the specific gravity of your brackish tank water and aim for a reading of 1.012. Specific gravity is a unit-less measure indicating the liquid's density in relation to the density of freshwater. Fresh water is represented as 1.000 and sea water is 1.023, so a reading halfway between these points is acceptable. Different species of brackish fish have their own requirements regarding salt levels, but if you are setting up a community tank, choose fish with similar needs.

    Brackish Water Fish

    • Spotted puffers, figure eight puffers, scats and monos are natural marine fish, but they can also survive in freshwater environments. These fish and others like them venture from salt water into fresh water to hunt for food, and as such, are able to thrive in brackish conditions. Domesticated brackish fish require the same foods that they would find in their natural habitat. Brine shrimp, plankton, krill and bloodworm are high in nutrients, but you can also feed them commercial flake or pellet fish food.

    Maintaining a Brackish Aquarium

    • Establish a water temperature of 70 to 85 degrees Fahrenheit depending on the species of brackish fish in your tank and maintain a pH level between 7.8 and 8.3. A coral or aragonite substrate will help keep the pH high and alkalinity in the required range. Tropical aquarium plants do not tolerate elevated levels of salt, although java moss, java fern and hair grass grow well in a brackish tank. Decorate your aquarium with rock caves and river pebbles, but take care with pieces of bogwood in a set-up with raised salinity, because the chemicals in wood can raise acidity and lower pH levels.