If it is not ich or another parasite, start the almost daily water changes and look below for treatment ideas. It is probably (down under) a bacterial problem/ Virus? Say, "Goodbye little fishies." But still change water.

Red swords will sometimes have white patches on their undersides. (Most fish are lightest there, it helps them blend with the sky or water when bottom dwelling predators look at them.)

Did you do a 20% partial water change after discovering the problem? All of us, me too, need to do that in that most illnesses are triggered by declining water conditions in the tank.

Funguses (there are several) tend to form on top of dead tissue. Sometimes a salt bath (marine level of a specific gravity of 1.023 on a hydrometer) until the fungus either lifts off or the fish is struggling to breathe.

Underneath the fungus, may be healing flesh which just needs the opening to oxygen rich water. There can also be bacterial diseases - hence the continued frequent partial water changes. If the flesh is reddish or off color, treating with an antibiotic after the fungus has lifted off might be good.

See:
Saprolegnia, diagnosis and treatment

http://www.fishdoc.co.uk/disease/fungus.htm

See also the Immediate help section on columnaris and Tetrahymena and also "Dead from nothing I can see" By angelhologram.
http://www.guppylog.com/story/2005/5/16/73157/9984

There is a lot of confusion between fungus and several skin clouding diseases. Even the pros do that sometimes. I was amused by the description on an old bottle of Jungle's Fungus Eliminator. They suggested that it would clear gray fungus (columnaris), red sores Furunculosis, fin and mouth rot, white film on eyes, red streaks in fins, and swim bladder disease. That bottle doesn't say what is in there, but I'll bet it is mostly an antibiotic. Most of those problems described are bacterial attacks, some the early stages of fin or tail rot. Bet they also want a 25% water change? They should ask for it for more days. ;)