Aquarium Salt promotes fish health by improving gill function, making it easier for fish to breathe. It also provides electrolytes that fish need to reach peak colouration and vitality. These electrolytes are lost each time the water in your aquarium is changed, and will need to be replenished with API Aquarium Salt. Use API Aquarium Salt in freshwater aquarium tanks when starting a new aquarium, and any time you perform a water change. Care should be taken when using salt in aquariums with live plants, as some plants may be sensitive. Directions for use: Add 1 rounded tablespoon for every 20 litres or 0.5 teaspoon for every 2 litres of aquarium water.