My guess is that the fish's lives would be cut short.From what I can understand Mollies and some Guppies can live in full salt water. Goldfish can do okay in Brackish conditions. Clown fish, I believe are tolerant of less than full-strength salinity.
So even without "magic water" some combinations of salties/freshies are perfectly achievable.
I don't think it could have been more then 55g either.That's crazy over stocked!!!^^^^^