Using Salt in a Freshwater Aquarium

Saltwater aquarium
Moto "Club4AG" Miwa/Flickr/CC BY 2.0

Next time your fish are sick, the remedy might not be farther away than your kitchen table. Ordinary table salt (Sodium Chloride or NaCl) is a useful remedy for the prevention and treatment of several freshwater fish diseases. It assists in the healing of injuries, promotes the formation of slime coating, improves gill function, reduces the uptake of nitrite, decreases osmotic stress, and is even effective against some external parasites.

However, some plant and fish species cannot tolerate much salt, so it must be used with caution. In these cases, some of the same benefits can be achieved by using commercial slime-enhancing (Stress Coat) products.

When to Use Salt

  • Nitrite Poisoning: The addition of a one-half ounce (1 level Tablespoon) of salt per gallon of freshwater (= 0.3% salinity) is beneficial for preventing nitrite from poisoning your fish in a newly set up tank.
  • Parasites: Many external parasites can be effectively reduced with the use of salt, particularly Costia (Ichthyobodo) infestations.

When to Avoid Salt

  • Live plants: If you have live plants in your aquarium, avoid using too much salt. Plants can be damaged with a relatively low dosage of salt, which is one reason it's best to treat sick fish in an adjunct hospital tank rather than your regular aquarium.
  • Scaleless fish: Scaleless fish species do not have the added barrier that scales provide, so they cannot tolerate much salt. The Corydoras catfish are particularly sensitive to salt; as are Tetras. Salt use in aquariums with these species should be no more than 1 level teaspoon per gallon of water (= 0.1% salinity).

Contrary to popular opinion, it is not advisable to add salt to your aquarium on an ongoing basis unless the fish are species that require brackish (partially salinated) water conditions.

Type, Quantity, and Duration of Salt

Common table salt is suitable; however, it should be non-iodized and contain no additives. Rock Salt or Kosher salt are excellent choices, as they are pure sodium chloride with nothing else added. Water conditioner salt, sold in 50 pound bags, is good to use for ponds, but should not contain prussic acid or other additives. The quantity of salt added to the water will depend on how and what it is used for.

A "dip treatment" is a short exposure to medication that is useful for the eradication of parasites. The high concentration of salt in the water will cause the parasites to come off the skin of the fish. For dips, freshwater fish can be placed in an aerated container of salted water with up to three percent salinity (10 level Tablespoons, or 5 ounces, per gallon of water) for 5 minutes, and up to 30 minutes, or until they lay on the bottom or roll on their side.

"Bath treatments" essentially mean that you are treating the entire quarantine tank; baths are useful for the treatment of stress, nitrite poisoning, and some parasites. Salt concentrations for a bath are lower, at one-half percent or less, (1 to 5 teaspoonsful per gallon of water = 0.1 - 0.5% salinity) and are maintained for up to three weeks.

Performing a Dip

When treating external parasites, a dip is the method of choice. Place five to ten level Tablespoons of salt in a clean bucket, then slowly add one gallon of water from the aquarium, while swirling the bucket to dissolve the salt. This will make a solution of 1.5 to 3.0% salinity. Once the salt is completely dissolved, place the fish in this bucket for five to 30 minutes. Observe the fish closely for the entire duration of the dip; if any signs of distress are observed, immediately return the fish to the original aquarium. Use an aquarium air pump with an air stone in the water to keep it oxygenated during the dip.

Performing a Bath

A bath is ideal when treating an entire tank for the prevention of nitrite poisoning or reduction of stress.

  • For the salt bath stress treatment, measure out one teaspoon of salt for each gallon of water in the tank (= 0.1% salinity). Using a small container, dissolve the salt in a small quantity of water taken from the tank. Once it is completely dissolved, slowly add the salt solution to the tank.
  • For the salt bath prevention of nitrite poisoning, measure out three teaspoons of salt for each gallon of water in the tank (= 0.3% salinity), then follow the same steps for dissolving and addition.

When using bath treatments, weekly water changes of 25 percent should begin one week after initial treatment. Do not add any more additional salt once bath treatments have begun. This will gradually dilute out the salinity of the water in your aquarium

Article Sources
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  1. Aquarium Water Quality: Nitrogen Cycle. Florida Department of Agriculture and Consumer Services