Salt is not advisable for any soft water fish.
Fresh water fish are called that for a reason, they live in fresh water. As the article points out, there is no benefit to using salt on a regular basis, it does not prevent anything. But it can be very harmful. It can be used to treat specific issues, but one must always first consider the fish. For soft water fish there are better remedies for disease.
I can assure you that salt is not going to prevent split fins. If it did this, we would all know it.