Using Salt in a Freshwater Aquarium

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

Next time your fish is 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 nitrate, and is even effective against some parasites.

However, some plant and fish species cannot tolerate salt, so it must be used with caution. In these cases, some of the same benefits can be achieved by using stress coat products.

When to Use Salt

  • Nitrite Poisoning: The addition of a one-half ounce of salt per gallon of freshwater is beneficial for preventing nitrite from poisoning your fish in a newly set up tank.
  • Parasites: Many external parasites can be effectively removed with the use of salt, particularly Costia infestations.

When to Avoid Salt

  • Live plants: If you have live plants in your aquarium, avoid using 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 tank.
  • Scaleless fish: Scaleless fish species do not have the added barrier that scales provide, so they cannot tolerate much if any salt. The scaleless Corydoras are particularly sensitive to salt; even a small amount could harm them. Tetras are also scaleless, salt-sensitive fish.

Contrary to popular view, 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 Salts or Kosher salts are excellent choices, as they are pure sodium chloride with nothing else added.

The quantity will depend on how and what it is used for. A dip is a short exposure that is useful for the eradication of parasites. For dips, a three percent solution is generally used for up to 30 minutes.

"Bath treatments" essentially mean that you are treating the entire tank; baths are useful for the treatment of stress, nitrite poisoning, and some parasites. Salt concentrations for a bath are lower, at one percent or less, and are maintained for up to three weeks.

Performing a Dip

When treating external parasites, a dip is the method of choice. Place four teaspoons of salt in a clean bucket, then slowly add one gallon of water from the aquarium, while swirling the bucket to dissolve the salt. 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.

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. 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 salty 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, 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.