Should Salt Be Added to Freshwater Aquariums?

Why on earth would fish hobbyists want to add salt to their freshwater aquariums? After all, these aquariums are supposed to contain freshwater fish species, such as catfish, which are intolerant of salt!

What The Experts Say About Adding Salt to Freshwater Aquariums

Some aquarium fish dealers recommend a routine dosing of salt as they believe that aquarium salt acts as a sort of “tonic” for freshwater fish, and that certain fish may thrive better when a small amount of aquarium salt is added to their tanks.

On the other hand, some fish experts do not advocate the permanent use of salt, unless the species has a natural requirement for it. The ill effect caused by the permanent use of salt, no matter how low the dosage, are yet unknown.

However when properly administered, salt does offer a number of scientifically valid benefits. Used correctly, it can treat health problems, tackle water quality problems, and minimize stress in fish.

What Is Aquarium Salt?

Aquarium salt is basically plain old sodium chloride, often with a bit of anti-caking agent to prevent it from forming into hard lumps. It does not contain additives like iodine or calcium silicate.

Marine salt, on the other hand, is much more complex. It contains special blends of minerals such as magnesium and calcium which make the water more conducive for marine invertebrates.

Salt is normally dosed in grams per liter or parts per thousand (ppt): 1g per liter equals 1ppt. knowing the volume of your aquarium or pond will enable you to calculate a suitable dosage.

To understand how to use salt in aquariums, we have to understand its effects on the osmoregulation of freshwater fish.

What is Osmoregulation?

Osmoregulation is the technical term for the physiological mechanism in fish that controls the amount of salt and water in their bodily fluids.

As its name implies, osmoregulation is based on osmosis, a process involving the movement of dissolved substances from a stronger concentration through a semi-permeable membrane to a weaker one. The body contents of freshwater fish are saltier than the water they live in, and their skin is semi-permeable. Osmosis will thus cause bodily salts in the fish to “leak” into the water.

Freshwater fish need to constantly take in water and extract salts from it to replenish what has been lost. This extraction is carried out by special cells in their gills. The constant intake of water means they also have to eliminate it by producing vast amounts of urine (some produce their own body weight in wee every three or four days!)

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