Salt is a generic name usually referring to sodium chloride, but more broadly any ionic compound, and is essential to life on Earth. Most biological tissues and body fluids contain a varying amount of salts. The concentration of sodium ions in the blood is directly related to the regulation of safe body fluid levels. Propagation of nerve impulses by signal transduction is regulated by sodium ions. (Potassium, a metal closely related to sodium, is also a major component in the same bodily systems). There are many different salts. For more details see salt chemistry on Wikipedia.
Usage in aquaria
Salt is used in the aquarium hobby for several reasons.
- Adjusting the salinity of water for brackish water or marine animals.
- Additive in freshwater tanks to aid the occupants due to osmotic pressure.
- To lessen ammonia or nitrite toxicity (usually in transporting fish).
- As an aid in treating disease or removing parasites.
It should be noted that the use of domestic 'table salt' is not recommended as this product often has unspecified anti-caking agents and other chemicals, such as iodine, in it. Sodium hexocyanoferrate (E535) is a common agent used to prevent table salt caking and this contains low levels of cyanide. But it is believed to be harmless in the very low levels used in freshwater aquariums for treatment use. Raw sea salt, or kosher salt, is generally acceptable, though always check the products ingredients.
Many freshwater plants do not tolerate any level of salt in the water and will soon perish.
- Pure freshwater with no salt has a specific gravity of 1.000
- Brackish water is often quoted as being a specific gravity of around 1.005
- Sea water has a specific gravity of around 1.020 to 1.024 (3.5% salt)
|Per Litre||Per Imperial gallon||Per US Gallon|
|Use||Recommended strength||grams||Level teaspoons (tsp)||Level teaspoons (tsp)||Time|
| Mild Ammonia/nitrite protection
(often used for shipping fish)
|0.1%||1g||1||.75||12-48 Hours or longer|
| General additive - nitrite protection
(Brown Blood Disease)
|Medium term parasite killer or swimbladder treatment||0.3 - 0.6%||3-6g||2.75-5.5||2.5-5||3–5 days|
|General heal, fungicide, repair of tissue||1%||10g||9||7.5||12 Hours|
|Short-term salt dip to remove parasites
swiftly followed by a clean water dip
|3%||30g||27||22.5||30secs to 10 minutes (check species)|
|Levels of salt for different classifications of water types|
|Marine sea water||35g||-||28||-|
(1 teaspoon = 4.7 grams, 1 tablespoon=14.2 grams)
Salt used for marine aquariums is not plain sodium chloride, but is in fact a complex recipe of many different types of salts. Various commercial mixtures of salt are available, all claiming to be the perfect salt for making up artificial sea water.
Typical commercial mixture for making ~1 litre of sea water:
|Chemical||Weight in grams|
|NaCl Sodium chloride||23.477g|
|MgCl2 Magnesium chloride||4.981g|
|Na2SO4 Sodium sulphate||3.917g|
|CaCl2 Calcium chloride||1.102g|
|KCl Potassium chloride||0.664g|
|NaHCO3 Sodium bicarbonate||0.192g|
|KBr Potassium bromide||0.096g|
|H3BO3 Boric acid||0.026g|
|SrCl2 Strontium chloride||0.024g|
|NaF Sodium fluoride||0.003g|
Then add pure water to make the final weight 1Kg.
Salt as a treatment
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.
Salt can be used to render levels of nitrite non-toxic for a limited period of time (3–6 weeks).
Animals that don't like salt
There are several species of freshwater fish that do not tolerate salt in the aquarium and these are listed here. It has been said some may tolerate up to 1ppt of salt for short periods but it will ultimately cause undue stress.
- Corydoras catfish
- Tetras - some species are particularly sensitive
- Elephant Nose
- Black Ghost Knife Fish
- Tiger Barbs
- Ram Cichlids
- Wild Discus
Animals that may prefer a level of salt in the water but can live without it
Fish that need a level of salt in the water and can not live without it
- PFK FAQ Salt article by vet Chris Walster - I've been warned off aquarium salts that contain sodium hexocyanoferrate. Why is this?
- Marine Aquaria book page 4 by L.A.J.Jackman, F.Z.S member of the Marine Biological Association U.K. Crediting Mr. F.A.J Armstrong and Dr. Wilson of the Plymouth Laboratory
- Koi vet: Salt - For Parasites & Nitrites!
- Corydoras World article on the use of Salt
Aquarium Wiki Articles
- The Salt of the Earth by Robert T. Ricketts
- The Use of Salt in Aquaculture
- Salt and Your Pond: Facts, FAQs and Myths (Part One & Two)
- Salinity - Wikipedia
- Salt - The Krib
- Brackish Water - Wikipedia
- Sea Water - Wikipedia
- Plants for brackish water
- Practical Fishkeeping - Frequently asked questions on using Salt
- AWT Marine Salt Mix Analysis
- Turquoise Wave - Using Salt to Treat Dropsy