You may occasionally hear mention of people suggesting you add salt to your fish tank. This does not mean add table salt to your fish's tank, as it will kill him. Regular table salt contains iodine. Humans need a small amount of iodine, but don't get it naturally in very many places, so salt companies decided to add it to table salt and market it as better for you. While this is good for you, it makes your table salt unusable for your tanks. Instead many pet stores sell aquarium salt. This is the same as table salt, but does not have iodine in it. Kosher salt can also be used as it contains no additives.

Using aquarium salt in your tank will help your fish produce a thicker slime coat. This clear mucus coating helps protect your fish from parasites, helps him heal from wounds and helps prevent nitrite poisoning.

If you have live plants or scaleless fish or tetras in your aquarium, you will want to shy away from using salt because these are sensitive to even small amounts of salt.

For bettas you can use a concentration of 1/2-1 tsp per gallon. Make sure other inhabitants of the tank are compatible with that concentration of salt. Aquarium salt does not need to be added every water change, but every 5 or 6 water changes.