04/02/2022
Adding Salt to a Freshwater Aquarium
When and When not to Add Salt
By Tony Griffitts
The practice of adding salt (a.k.a. Sodium Chloride, rock salt, table salt, solar salt, aquarium salt) to freshwater aquariums has been around almost as long as the hobby. There are several reasons why hobbyists add salt to the aquarium, stress reduction, medicating, adding hardness, and for fish commonly found in brackish water. It has become a common practice for employees of big box stores to tell all of their freshwater customers to add a teaspoon of salt per 10 gallons (38 l). This is not a practice most advanced hobbyist partake in, nor one recommended. Before you add salt to a freshwater aquarium, you should understand why you are doing so, and any possible side effects.
Freshwater
Most wild populations of freshwater fish and plants in the hobby come from rivers and lakes that have very little if any detectable salt. Freshwater fish are adapted to water with salt content that is measured in parts per million (ppm), versus seawater that is measured in parts per thousand (ppt). My local water supply comes from surface water and it averages less than 3 ppm total sodium. That means that out of one million parts, less than 3 are salt. In many cases freshwater has very low salt content, and in some areas of the world, like tropical rain forests, it can be so minute that it is undetectable.
Fish and Plants
Freshwater fish and plants have evolved to live in an environment that has very little salt, and because of this some are very sensitive to salt. Most freshwater plants do not tolerate much salt at all, and if you are trying to keep live plants, salt as a general rule should be avoided. Some species of fish from very soft water, like Plecostomus (sucker mouth catfish) do not tolerate much salt either, and the addition of salt with these fish should be avoided.
