Also try the flashlight trick on the sick male.  If there's a clear layer under the skin and over the organs, he has edema.  Edema can occur with many illnesses, including bacterial infections, which can also cause redness and white areas.  Until Jancy said "fungus", I was thinking "bacterial infection".  But then I have a little experience with bacteria and none with fungus, so that may be coloring my conclusions.

Mac, can you make a better guess as to whether to use antibiotics or antifungals?  Either way, definitely keep the water pristine (nitrates under 10, not 20).