To salt, or not to salt?

Salt is a generic name usually referring to sodium chloride, but more broadly any ionic compound and essential to life on Earth!

There are a lot of misconceptions about the various salts available for aquarium use. Table salt is nothing more than Sodium Chloride (NaCl) which comes in iodized and non-iodized forms and has unspecified anti-caking agents and other chemicals such as iodine. Non-iodized salt may or may not be the same as aquarium salt (it depends on the brand).

Aquarium Salt is very similar to table salt in as much as it is made of Sodium Chloride (NaCl) however it lacks anti-caking ingredients and iodine. Epsom Salt is Magnesium Sulfate (MgSO4).

Salt is used in the aquarium hobby for several reasons:

  1. Adjusting the salinity of water for brackish water or marine animals
  2. Additive in freshwater tanks to aid the occupants due to osmotic pressure.
    – Osmotic pressure can be best described as the water trying to dilute the fish’s body until both sides are equal. Freshwater fish therefore have to constantly eliminate the water through respiration and urine. Stress protecting additives aid this function but if salt is used, 1 teaspoon per 1900 litres is sufficient.
  3. To lessen ammonia or nitrite toxicity (usually in transporting fish or if your filter suddenly stops working or you’ve just set up a new tank and nitrite levels spike)
    – Salt can be used to render levels of nitrite non-toxic for a limited period of time (3–6 weeks)
  4. As an aid in treating disease or removing parasites
    -Salt can be used to kill off Ich, Costiasis, Trichodina and other parasites. There are some studies indicating that the usual 1% solution of salt is becoming ineffective and people are resorting to using levels of up to 3% today. A salt bath will stimulate the protective slime coat which will further enhance the fish’s’ ability to cope with the disease

Salt does not evaporate! It can only be removed by water changes. Plants will not survive higher concentrations (the lethal point for plants is reached at about 1000 mg/l of salt and one teaspoon of salt equals approx. 5500mg). It does interfere with the osmotic regulation of fish and plants and we suggest it should be left alone! Nature regulated that part herself; by creating freshwater, brackish and saltwater fish. The low beneficial amount of salt will not have any benefits in addition to water conditioners and/or stress coats already used for water treatments and because of the potential hazards to the health of your fish and plants we do not recommend the use of salt in freshwater aquariums.

Animals that don’t like salt:
There are several species of freshwater fish that do not tolerate salt (it has been said some may tolerate up to 1ppt of salt for short periods but it will ultimately cause undue stress). These include Corydoras catfish, Plecos, Tetras (some species are particularly sensitive), Elephant Nose, Black Ghost Knife Fish, Tiger Barbs, Otocinclus, Ram Cichlids, and Wild Discus.

Animals that may prefer a level of salt in the water but can live without it:
Livebearers, Indian Glass fish and Certain Puffer species

Fish that need a level of salt in the water and can not live without it:
Marine Fish and Brackish Fish

Tables courtesy of and

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