Salt and Its Uses

Not open for further replies.


Viviendo la vida loca!
MFK Member
The Use of salt (sodium chloride, NaCl) in the freshwater aquarium or pond.

What is salt?

In the broadest sense a “salt” is the chemical compound formed when an acid reacts with a base. There are many “salts” in our everyday lives: baking soda, or sodium bicarbonate, NaHCO3, and washing soda, soda ash or sodium carbonate, NaCO3, are two examples. The more familiar table salt or sodium chloride, NaCl, is a salt that is formed when hydrochloric acid (a.k.a. muriatic acid) reacts with sodium hydroxide (a.k.a. lye). Common salt exists in several forms and most of these are found in the modern home. There is the stuff found in the salt shaker in the dining table, there is the rock salt we use to melt ice and snow, and there is the water softener salt we use to recharge our home water softener zeolites.

Are all forms of common salt essentially the same?
The short answer is “yes”. For all practical purposes these different forms of household salt are the same. The basic differences are found in the purity and the additives. Rock salt, basically, is just the material as it comes from the salt mines or evaporation ponds. It contains greater or lesser amounts of impurities and is not suitable for human ingestion. Water softener salt is a purified form that is usually pressed into pellets. Except for its physical form it would be suitable for use in cooking; it is also a bit pricey to be using as an ice-melt.

Table salt comes in two basic formulas; iodized and non-iodized. The latter is used where natural iodine content in the drinking water and other food sources may not be sufficient to prevent human goiter (a disease condition of the thyroid gland). Table salts also contain one or more additives that prevent them from caking, and therefore, free flowing, in a humid atmosphere. “When it rains it pours.”

Are the additives in table salt harmful in aquariums or ponds?
The short answer is “no”. Neither the small percentage of iodides nor the anti-caking additives can be considered to be dangerous when the salt is used in ponds or aquariums. There is no valid reason to use only non-iodized salt yet this is always a hot topic for discussion and argument among aquarium hobbyists. In reality, the minuscule amount of iodide that would end up in a treated pond or aquarium is likely to be beneficial (as a potential source of essential iodine for both certain plants and animals) and certainly not harmful. Fishes can suffer from goiter (= iodine deficiency) also.

How useful is salt used in aquariums and ponds?
From the number of aquarium hobbyists and pondkeepers who use salt one would have to assume that it is one of the best, if not the best, treatment to use for all kinds of known and unknown diseases. The reality is quite different.

It is quite possible that the unwarranted reliance upon salt treatments has resulted in more fish losses than the diseases themselves. This is because there is a common misunderstanding among aquarists and pondkeepers that salt is a good disinfectant, antibacterial, antifungal and/or antiprotozoal drug. At the concentrations commonly used in aquariums and ponds it is none of these things. As a reliable disease treatment and/or preventative salt is essentially useless.

For what is salt useful?
Primarily, salt can be used for two different, but related problems. The first is the treatment of nitrite, NO2-, poisoning, and the second is the treatment of osmoregulatory stress. In both cases it is the property of sodium and chloride ions to be transported across the gill membranes, from the water, and into the blood of the fishes.

Osmoregulatory stress can result when fishes are transported or when they are removed from water of one osmotic pressure and placed into one which is significantly different. In general aquarium and pond practice, where one is working only with freshwater fishes, the problems associated with osmoregulatory stress are essentially nil and therefore of little concern.

For nitrite poisoning, salt can impart protection to the fishes. This happens only if the salt content is such that the chloride ion’s concentration is about 30 times that of the nitrite ion concentration in the water. Typically, nitrite becomes toxic at about 0.1 mg/L. This means that the chloride ion concentration would have to be at least 3.0 mg/L. This concentration translates into one of about 5.0 mg/L of salt (NaCl is 60.66% chloride, Cl-); this is equivalent to 18.7 mg/gallon. A teaspoon of table salt is about 5.5 grams (or 5,500 mg); a teaspoon of table salt would be sufficient to protect fishes living in approximately 294 gallons of water! A standard treatment of NovAqua will typically provide enough protection.

For simple osmoregulatory stress protection, on an indefinite basis, one can use 1 to 3 mg/L of salt. This would be equivalent to one teaspoon of salt added to 1,453 to 484 gallons of water!

What about disease treatment with salt?
In his book, Fish Medicine (W.B. Saunders Company, 1992), Michael Stoskopf lists salt at a concentration of 22 mg/L (= 83.27 mg/gallon), as a dip, for 30 minutes to control fungal infections and protozoal infestations (specifically Epistylis sp.). This treatment level is equivalent to 1 teaspoon per 66 gallons of water! Stoskopf, lists no other treatment uses, and to use salt in place of reliable and safe treatments like Rid-Ich+ for treating diseases, like ich, is simply not justified.

To use salt at higher levels (e.g. 1 teaspoon per gallon) than those indicated by the literature is also not justified. Higher levels, especially on freshwater fishes such as characins (tetras), cyprinids (goldfish and koi) and catfishes, will act as an irritant and thereby stress the fishes. Fishes such as livebearers and cichlids can, likely, tolerate much higher levels of salt (some species of livebearers and cichlids actually enter seawater).

From Aqua Science research group website!


Viviendo la vida loca!
MFK Member
Another source of information.

The Use of Salt in Aquaculture1

Ruth Francis-Floyd2
Salt, also known as sodium chloride or NaCl, has many potential applications in fish production. It effectively controls some parasites, minimizes osmoregulatory stress during transport, and prevents methemoglobinemia (brown blood disease) in channel catfish. While the Food and Drug Administration (FDA) has not approved the use of salt in aquatic animals, FDA considers the use of salt in aquaculture to be of low regulatory priority. The agency does not regulate the use of salt to control salinity.


Salt is the generic term applied to the ionic or mineral component of water. All water except distilled or deionized water contains some salt. Minerals found in water have many important physiologic functions in fish. For this reason, fish should never be placed in 100 percent distilled or deionized water.
Although seawater is composed of many different salts, sodium chloride is the predominant one. Marine animals must be maintained in a saltwater solution that contains the micronutrients found in natural seawater. A number of products containing these nutrients are commercially available. Since the micronutrients present in sea salt are not critical for the survival of freshwater fish, either noniodized table salt or rock salt (suitable for consumption by humans or livestock) may be used for salt "treatments" in these species.


The effects of salt on fish are determined both by salt concentration and duration of exposure. Seawater contains 3 percent salt by weight; this is equivalent to 30 parts per thousand (ppt) or 30,000 parts per million (ppm). Some parasitic infestations of freshwater fish may be effectively eliminated by dipping fish in a seawater solution for 30 seconds to 10 minutes, depending on the species. Weaker solutions containing 0.5 to 1.0 percent salt may be used as a bath for several hours to eliminate some freshwater parasites. Concentrations of 0.1 to 0.3 percent may be used to enhance mucus production and osmoregulation in freshwater fish during handling and transport. Very weak salt treatments, measured in ppm, may be used to control methemoglobinemia in some freshwater fish species.


Used in proper amounts, salt effectively controls protozoans on the gills and skin of fish. In many instances, however, too little salt is used, rendering the treatment ineffective. The duration of treatment is used to determine the appropriate salt concentration.

A 3 percent salt dip effectively removes protozoa from the skin, gills, and fins of freshwater fish; it also enhances mucus production. Depending on the species, fish can remain in a 3 percent salt solution from 30 seconds to 10 minutes. In general, fish should be left in the salt solution until they lose equilibrium and roll over. When this happens, the fish should be quickly removed from the salt solution and placed in clean, untreated water. Because some species (notably, some tetras) do not tolerate salt well, a bioassay (a test to determine safe concentration) should be conducted before large numbers of these fish are treated. A similar benefit may be obtained by dipping marine fish in fresh water. Marine protozoa burst when placed in fresh water, effectively removing them from the external surfaces of fish. Marine fish should be left in fresh water for no more than 10 minutes, then returned to a clean seawater environment.

If dipping is not feasible, freshwater fish may be placed in a brackish water (i.e., 1 percent salt) solution for 30 minutes up to several hours. This procedure produces the same effects as a saltwater dip; that is, it removes external parasites (protozoa) and enhances mucus production. It also benefits fish recovering from skin wounds.

Finally, a light solution of 0.01 to 0.2 percent salt may be used as a permanent treatment in recirculating systems. Such levels are quite effective in eliminating single-cell protozoans. Most fish can tolerate prolonged exposure to salt at these concentrations; however, tetras and fish that navigate by electrical field (e.g., elephant nose) should not be maintained in salt.


When freshwater fish are transported and handled, they are forced to expend extra energy for osmoregulation (water balance) unless salt is added to the transport water. Freshwater fish tend to overhydrate when held in fresh water during shipping, due to the influx of water across the gills and into the bloodstream. To compensate for this water imbalance, fish pump excess water back across their gills. Increasing the salt concentration of the transport water inhibits this process, making depletion of energy reserves less likely. Salt may be added to the transport water to increase salinity from 0.1 to 0.3 percent (1,000 to 3,000 ppm, or 3.8 to 11.4 g/gal), minimizing the osmoregulatory stress on fish during shipment.

If fish are being transported from one site to another -- for example, from a pond to smaller tanks or vats within a building -- salt may be added to the receiving water. An easy way to accomplish this is to add a small amount of water to the receiving tank, then add salt to create a 3 percent solution (30 ppt or 30,000 ppm); when fish are added to the tank, it should be filled with water. Short-term exposure to a high concentration of salt produces an anti-parasitic effect; longer exposure to a lower concentration of salt helps to stabilize osmoregulation and increase production of the mucus covering the skin, which may have become damaged during handling.


Freshwater fish, particularly channel catfish, are susceptible to brown blood disease, which is caused by an accumulation of nitrite (N0 2 ) in the water. Although most studies conducted on brown blood disease have used channel catfish as a model, many other freshwater species are also susceptible to the condition. A detailed discussion of nitrite toxicity is provided in a separate IFAS publication. Following is a brief review of the use of salt to prevent and treat brown blood disease.

In freshwater systems, nitrite toxicity is directly related to chloride (Cl - ) concentration, since nitrite (N0 2 - ) and chloride (Cl - ) particles compete for space to cross the gills and enter the bloodstream (see Figure 1 ). As chloride concentration in the water increases, nitrite's ability to enter the bloodstream decreases.

Figure 1 .

The critical component in brown blood disease is the chloride (Cl - ) portion of the salt molecule (NaCl). For this reason, a test to measure chloride concentration (ppm) should be used rather than a test that uses a hydrometer or refractometer to measure salinity.

A minimum chloride concentration of 20 ppm is recommended to prevent nitrite toxicity among channel catfish in ponds. Most ponds are supplied with water containing at least 20 ppm Cl - ; however, salt should be added to ponds containing less than 20 ppm Cl - to increase the chloride concentration to the desired level (see Table 1 ). For each acre-foot of water in the pond (1 surface acre, 1 foot deep = 43,560 ft 3 ), 4.5 pounds of salt adds 1 ppm chloride.

Salt may be used to minimize mortality and facilitate recovery of fish that develop brown blood disease. For every ppm of nitrite present, 6 ppm chloride should be used to control the disease. As described earlier, the producer must determine the required chloride concentration, adding 4.5 pounds of salt per acre-foot of water for each ppm Cl - needed (see Table 2 ).


Salt has many uses in modern aquaculture. Although FDA has not approved the use of salt as a "drug" to treat fish, the agency has designated salt as a compound of "low regulatory priority." Salt is inexpensive, readily available, and, when properly administered, safe for use in freshwater fish. Therapeutic uses for salt include parasite control, osmoregulatory stabilization, mucus production, and alleviation of methemoglobinemia in freshwater fish. Salt concentration should be based on intended use, duration of exposure, and tolerance of the species to be treated.


Table 1.
Table 1. Using Salt to Prevent Brown Blood Disease
1.Check chloride concentration in pond. If <20ppm, add salt as shown below.

2.Determine concentration of chloride [(Cl-)] needed:
20 - [Cl-] = [Cl-] needed

3.Determine volume of pond in acre-feet
(1 ac-ft = 43,560 ft3).

4.For each ppm Cl- needed, add 4.5 lb salt per acre-foot of water.

1.A fish pond has a natural chloride concentration [Cl-] of 10 ppm.

2.Chlorine needed = 20 -10 = 10 ppm.3.To determine volume, measure the pond. It is 100' x 200' x 6' deep = 120,000 ft

3.120,000 ft3 / 43,560 ft3/ac-ft = 2.75 ac-ft.

4.Amount of salt to add is:
= [Cl- needed] x Vol (ac-ft) x 4.5
= 10 x 2.75 x 4.5
= 124 lb of salt needed.

1. Salt should be added to a fish pond containing less than 20 ppm chloride.
Table 2.

Table 2. Using Salt to Control Brown Blood Disease1.Measure nitrite concentration ([NO2-]).

2.Measure chloride concentration [(Cl-)].

3.Determine chloride concentration necessary to meet the recommendation of 6 parts chloride to each part nitrite:
6 x [NO2-] - [Cl-] = chloride needed.

4.Determine volume of pond in acre-feet
(1 ac-ft = 43,560 ft3).

5.Add 4.5 lb salt per acre-foot for each ppm chloride needed.Example:1.[NO2-] = 10 ppm.2.[Cl-] = 20 ppm.3.[Cl-] needed = 6 x 10 - 20 = 40 ppm.4.Pond is 100' x 200' x 6' = 120,000 ft

120,000 ft3 / 43,560 ft3/ac-ft = 2.75 ac-ft.

5.Amount of salt to add is:
= [Cl- needed] x Vol (ac-ft) x 4.5
= 40 x 2.75 x 4.5
= 495 lb of salt needed.

Example 2. To control mortality from brown blood disease, increase chloride concentration to 6 times that of nitrite. Add salt to increase chloride level.


1. This document is Fact Sheet VM 86, one of a series of the Department of Large Animal Clinical Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Reviewed November 1995. Please visit the FAIRS Web site at

2. Ruth Francis-Floyd, D.V.M., M.S., associate professor, Department of Large Animal Clinical Sciences, College of Veterinary Medicine; Department of Fisheries and Aquatic Sciences; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
  • Like
Reactions: Comanswoodwork
Not open for further replies.