From The Aquarium Wiki
Revision as of 13:28, 12 November 2013 by BACbKA (talk | contribs) (Usage in aquaria: E535)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

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[edit]

Salt is used in the aquarium hobby for several reasons.

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.[1] 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.[citation needed]

  • 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)

Using salt[edit]

Using Salt in an Fresh Water Aquarium as an aid
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)
0.3% 3g 2.75 2.5 12-24 Hours
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
Brackish water 0.5-30g - - -
Marine sea water 35g - 28 -

(1 teaspoon = 4.7 grams, 1 tablespoon=14.2 grams)

Marine salt[edit]

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.

This yields sea water of salinity 34.5‰, pH between 7.9 and 8.3.[2]

Salt as a treatment[edit]

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.[3]

Salt can be used to render levels of nitrite non-toxic for a limited period of time (3–6 weeks).[citation needed]

Animals that don't like salt[edit]

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.

Animals that may prefer a level of salt in the water but can live without it[edit]

Fish that need a level of salt in the water and can not live without it[edit]


  1. PFK FAQ Salt article by vet Chris Walster - I've been warned off aquarium salts that contain sodium hexocyanoferrate. Why is this?
  2. 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
  3. Koi vet: Salt - For Parasites & Nitrites!
  4. Corydoras World article on the use of Salt

Aquarium Wiki Articles[edit]