I've never liked adding salt to betta tanks, unless it is in teeeensy-eeeensy amounts. It does have some healing effects, but it raises the hardness of the water too much (IMO). I started adding salt to my betta's tank when he was looking a little down and he just got worse. When I removed the salt he perked up quite a bit. The reason I suggested short salt-water baths is because it's a quick way to expose them to the healing nature of salt without the long-term risk of hard, alkaline water.