I am with Agreement, no salt for fish. I have read many articals by Biologists on this and most say nay. There is no need, it may cause more harm in the long run.
If you want healthy fish, do more water changes, either once to twice a week. Many had always felt that using salt was a tonic and would help improve the health of the fish. Well this is being disproven and just general maintence to your tank is needed.
Replace filters often and do weekly water changes and you will have healthy fish.