Need to know water stats, ammonia, nitrite, nitrate, and pH. Water stats are the first place to look when trying to figure out what is the cause of a disease.
It sounds like slime disease, aka cosista.
I am not the author of the following information.
Costia
Symptoms:
Infected fish have soft, film-like skin turbidity. A grayish white film of excess mucous covers the entire body of the fish including the eyes. Severe infestations can lead to skin inflammation and deterioration. Reddening of the skin and bleeding, most often occurs on the underside of the mouth and the pectoral area of the body. Sick fish often rub or scratch against objects in the aquarium in an attempt to relieve irritation. Severely infected fish may become reclusive, listless, lie on the bottom of the aquarium and stop feeding.
Cause:
The parasitic flagellates Costia necatrix and Ichthyobodo necatrix. Costia is a small bean-shaped flagellate which attaches tightly to all areas of the skin, destroying the flesh. This parasite can only survive for approximately one hour without a host and does not tolerate temperatures above 86 - 90 F.
Treatment:
Raising the water temperature to 86 - 90 degrees may be helpful if your fish can tolerate the high temperatures. Quick Cure, Formalin, Malachite Green and Copper Sulfate are the drugs of choice for Costia. Costia infestations are highly contagious. All fish, including the aquarium, should be treated.
