Adding aquarium salt to your tank is an important part of maintaining a healthy fish habitat. Generally, the amount and frequency of adding aquarium salt will depend on the type of aquarium you have, as well as the species of fish that inhabit it. Most freshwater tanks require between 0.1-0.3% salinity levels, while saltwater tanks should be between 1-2%. To achieve these levels you may need to add up to 3 tablespoons per 10 gallons every two weeks or so, depending on how much water evaporates from your tank during this time frame. Additionally, if you notice any changes in behavior or appearance among your fish after adding the salt then it might be best to adjust either the concentration level or frequency at which you add it accordingly.