Aquarium Salt (Sodium chloride) in Freshwater Aquariums

The use of Sodium Chloride more commonly known as just plain salt seems to be a constant source of controversy among aquarists, especially here on the internet. What is interesting to me and my colleagues in the professional aquarium maintenance, design and research business is that the way this controversy has “swung” from you MUST use salt to the now current fad propagated by many forums and articles including such about.com to RARELY use salt.
Unfortunately both views are based on misunderstandings of the term of what salt is and what fish need “salts” for as well as a lack of understanding and reading of research about this subject.

What is “Salt”

I will start with some basic definitions of what “salts” are (further reading beyond this article is needed here, so please follow links/resources/references).
Basically a salt is a neutral compound composed of cations (positively charged ions) bound to anions (negatively charged ions).
A little more in depth description is that “salts” are ionic compounds held together by electrostatic attraction of positively charged metal cations and the negatively charged anions. These Ions can be single atoms, as in sodium chloride, or more complex groups such as calcium carbonate.
What I am driving at is that salts consist of more than just Sodium Chloride and that “salts” in general are IMPORTANT electrolytes necessary for biochemistry and osmoregulation in fish without which fish and other biochemical processes would cease.
Please reference these two articles for further reader as to this subject:
PROPER OSMOTIC FUNCTION- ELECTROLYTES
CALCIUM, ELECTROLYTES, AND MAGNESIUM IN AQUARIUMS; How to maintain a Proper KH & PH, why calcium and electrolytes are important.

Sodium Chloride and other Salts in Aquariums

This where the controversy begins in my opinion is should aquarium salt sodium chloride) be used and if not, what will takes its place for necessary electrolytes.
First I will start off by stating again that ALL living organisms need certain electrolytes for biochemistry (the before mentioned resources help explain this).
I have read many scientific studies as well as performed many experiments over the years in the use of different salts including sodium chloride.
I will start off by stating that a successful aquarium CAN be kept without sodium chloride HOWEVER other salts MUST be present such as Calcium carbonate, otherwise your fish will have lower disease resistance and other physiological problems.

Where this gets controversial is with freshwater plants, catfish, goldfish and livebearers such as mollies.
Starting with each of the above, let’s take a look them specifically:
*Freshwater Plants; As many articles state correctly, many freshwater plants (not all though) have a low tolerance for sodium chloride, so care must be exercised in the use of sodium chloride (NaCl) with many plants present. Most freshwater plants can tolerate up to 1000 mg. per liter of sodium chloride and since a teaspoon I roughly 5500 mg. that equals one teaspoon per 5.5 liters of water or 1.45 gallons (one gallon = 3.785 liters). This is approximately 1 tablespoon per 5 gallons. Please keep in mind that this is the upper reaches of many plants tolerance, so a lower amount would be better.
This said, I generally have used very little sodium chloride salts in my planted aquariums (Anubias one of the exceptions), however the plants still require other electrolytes (salts) so one must make sure that calcium carbonate, magnesium and other necessary salts are present.

*Catfish, Tetras, Elephant Nose, etc.; This is an area where my own research as well as university level research does not “mesh” with current popular opinions/fads. While it is true that Catfish, Tetras, and fish such as Elephant Nose do not tolerate salt well, they still MUST have some electrolytes and can tolerate some salt, at least in short tem doses. While fish such as tetras and fish that navigate by electrical field do not do well in higher doses of salt (NaCl), these fish can tolerate short term doses of salt such as after introduction of new fish for aid in disease resistance, transport or aid in disease treatment. Generally long term sodium chloride use should be kept to levels under 500 mg. per liter or less, I recommend no more than 1 teaspoon per 5 gallons for these fish (this is one TEASPOON, not tablespoon!).

Since there is little money for really good studies for most areas of aquarium keeping I (and others serious about really good research) must look to outside sources for information (this includes other areas such as Aquarium Lighting and many other poorly researched within the aquarium industry subjects).
Where I am going with this is that outside of my own tests and side by side studies (admittedly not to university level standards) most good research as to salt (NaCl) comes from studies in food grade fish such as Channel Catfish. Although Channel catfish are not Corydoras Catfish, these studies are not 100% as to extrapolate of the results, however based on my own studies as well they are still VERY useful. The most current studies I have read show that Channel Catfish CAN tolerate salt in surprisingly high amounts for at least short periods of time. In fact studies have shown that treatment of Channel Catfish for Columnaris when sodium chloride is used vastly INCREASED the survival rate! These studies showed increased survival in concentrations between 1000 and 3000 mg. per liter.

Bringing this back to aquarium keeping and my own studies/results as per catfish, I found no problems in short term use up to 2 tablespoons per 5 gallons and long term use up to one teaspoon per 5 gallons.

Goldfish Gold fish are a from a family of fish that include koi and carp. The common goldfish (Carassius auratus) and its fancy variations are fish based on my own experience that do better in water that contains moderate amounts of minerals and electrolytes. This includes a GH (for Calcium, magnesium and more as well as some sodium chloride salt. My clients goldfish have always had more longevity and less incidence of disease when the GH is 200 ppm plus and I have kept 1 tablespoon of salt per 5 gallons of water. In fact a government study shows INCREASED survival rates when chronic salinity levels were increased up to 6000 mg. per liter (6 ppt). Please reference this site bought to my attention by a knowledgeable colleague:
http://cars.er.usgs.gov/posters/Nonindigenous/Salinity_Tolerance_of_Goldfish.
I will also note as per goldfish that these are a fish that I have performed several tests/studies as per the use of salt, use of UV Sterilization and improved Aquarium Redox.
These facts fly in the face of the many anecdotal postings of what is best for healthy goldfish.

Livebearers such as Mollies; This is another area where I find some miss-information. Most aquarists would agree that mollies will do fine with sodium chloride salt in their aquariums, however what many aquarists miss is that mollies do not all come from areas with NaCl in their water but ALL mollies and livebearers in general do and must have other electrolytes such as Calcium Carbonate and Magnesium in their water as well as buffers such as sodium bi-carbonate.
Personally I have had the best results with my livebearers with a GH well over 200 ppm (for calcium/magnesium), a KH over 150 ppm and finally 1 tablespoon of sodium chloride per 5 gallons.
Please see this article for more: “Keeping Molly Fish in Aquariums”

A Few Facts, Uses and Myths About Salt in Aquariums

*There are other salts/electrolytes such as Calcium Carbonate that are important for proper osmoregulation, disease prevention (and even treatment) in freshwater aquarium fish.

*Sodium Chloride is useful for Brown Blood disease (nitrite poisoning) in freshwater fish as well as for a stress reliever in fish transport. A minimum chloride concentration of 20 ppm is recommended to prevent nitrite toxicity. Please see this article for more: http://edis.ifas.ufl.edu/VM007

*Sodium Chloride salt can help prevent and even treat many diseases from Ich to Columnaris, however this is an area where many go overboard too much the other direction as sodium chloride is NOT a cure all, especially when it comes to virulent Ich infestations.

*Sodium Chloride Salt can be safely used in most all freshwater aquarium applications provided proper levels are observed and as noted earlier other “salts” are also employed either with or without sodium chloride.

*Sodium Chloride aids in slime coat generation (often better than over touted slime coat products, especially those that place a slime bandage on the fish). However it should be noted that there are other electrolytes that aid in slime coat generation as well potassium.
Please see this article for more about water conditioners:
“Aquarium Answers; Aquatic water conditioners”

*Sodium Chloride does not dissipate, meaning that generally only water changes will remove salt. For example if you are using salt (NaCl) in your 20 gallon aquarium and you change 5 gallons of water you need ONLY add salt for the 5 gallons changed, not the 20 gallons of aquarium water otherwise your salt levels will build up with time.
It is noteworthy that very small amounts of Sodium Chloride are used in biological processes within the aquarium/inhabitants, however this amount is not worth adding more salt for.
In the case of some other salts such as Calcium carbonate and potassium, these will get depleted a higher rater by biological processes and will often need to be replaced depending on water change amounts, bio load, tap water (or other replacement water chemistry), tests, etc.

SUMMARY

I will some this up by saying that those who say you should not use sodium chloride salt in your freshwater aquarium (including with Catfish, Tetras, etc.) and those who say you should always use salt (NaCl) are only HALF RIGHT. I would certainly agree that there was (and still is) a segment of the aquarium keeping hobby that thinks sodium chloride is the cure all for everything all the while ignoring important other “salts” such as Calcium Chloride. However the current “No Salt” fad is also ignoring certain facts not only about sodium chloride but about the other important electrolytes as well. My own years of experience and tests along with research and many of my professional aquarium keeping colleagues bears this out.

When salt is used the use of iodized salt that is often found in kitchen cupboard is not the best choice, however in a pinch it is not a terrible choice as is often described. If the small amount of salt that is needed in a freshwater aquarium is used the iodine (which is also a necessary nutrient for fish in small quantities as in humans) is not likely to cause any problems. Common table salt also has anti-caking agents such as sodium aluminosilicate which is main reason to avoid table salt as this ingredient may cause increases algae growth (other anti-caking ingredients include potassium ferrocyanide and calcium carbonate).
I prefer either plain rock salt, marine salt (of which the additional major and trace elements are actually beneficial to many freshwater fish), or products such as SeaChem Cichlid Salt which (similar to marine salt in concept) contains added minerals/electrolytes of which when used in the small amount of salt one should use sodium chloride are actually beneficial for the vast majority of freshwater fish.

Other Resources
http://edis.ifas.ufl.edu/VM007
http://www.int-res.com/articles/dao/21/d021p171.pdf
http://cars.er.usgs.gov/posters/Nonindigenous/Salinity_Tolerance_of_Goldfish
http://www.ca.uky.edu/wkrec/SaltStressCatfish.pdf