It sounds like the NH3 attack was fairly severe. The whitish patches you described is typical of NH3 poisoning, where the skin actually starts breaking down. This can often look like disease and, of course, such stress and cell destruction can be complicated by disease taking advantage of the weakening fish. Gills and internal organs (including the brain) are usually damaged as well. Recovery is not guaranteed.
Unless your tank has dormant parasites, such as Ick, I would focus upon minimizing bacterial infections with a broad spectrum antibiotic such as Kanaplex or Sulfaplex, or others. Make sure that you remove any chemical media (such as carbon) from your filter. With Kanaplex or Sulfaplex, you don’t need to worry about your BB, so leave the biomedia in your filter, but I don’t know about other brands of antibiotics without checking their websites.
Make sure your gas exchange is good. The waters’ surface should be rippling without breaking the surface. I assume that you keep temperature within about 5 oF of tank water temps during w/c’s and chlorine/chloramine is addressed as well. If you have a TDS meter (they are cheap), it is a good idea to keep tank water within 10% or 50ppm, whatever is less, of pre-water change levels to minimize stress.
Get that salt out of your water. We did that in the 'olden days' before we knew better. It will send your TDS soaring, which is a great stress inducer. Make daily water changes using the TDS guidelines, above, until your TDS reaches normal (pre-salt) levels.