With all the advancements in the aquarium hobby, it is sometimes easy to overlook the simple, basic treatments aquarists have used since fish were kept in aquariums. One of the most basic is the addition of aquarium salt to the freshwater aquarium. While the exact mechanism of benefit is not completely known, fish have been shown to do better with small amounts of salt added. You want to use a true aquarium salt or kosher salt to avoid adding other additives to the aquarium, like excess potassium or iodine. For most tropical fish, you would dose one tablespoon of salt for every 5 gallons. You want to calculate the amount of salt to use by the total volume of the aquarium, but after the initial dose, you will only want to add salt when you do a water change. If you remove 10 gallons of water, you would want to add just 2 tablespoons to dose the 10 gallons. There would be no need to re-dose the water already in the aquarium.
The benefits of adding salt to the freshwater aquarium include providing sodium and chloride ions for the fish, stimulating the production of the natural slime coat that is the fish’s first line of defense against parasites and bacteria, plus inhibiting the uptake of toxic ions like nitrite by the gills of the fish. Many freshwater fish come from waters rich in ions, i.e. livebearers and of course brackish water fish. Most Tetras and Barbs are tolerant of standard dosing levels, though some of the Loaches and Corydoras Catfish sometimes show stress when salt is added. Freshwater plants can also tolerate normal dosing but might whither under higher levels. So don’t forget, aquarium salt is a simple addition to the freshwater aquarium that can benefit the health of your fish.