No, salt is only good for mollys because they are known to inhabit brackish environments. Fish that don't live in slightly salty or very salty environments (like platys and goldfish) will gain no bennefets from salt usage unless it is for the treating of certain deseases and parasites. Goldfish do not inhabit salty enviroments in the wild, and salt will have no benefet for them.
Tonic salt does pretty much nothing for fish (its pretty useless really), you really need marine salt for salt treatment, which is a lot different from tonic salt.