Hi Henry,
If these are coldwater fish tehn in all likelihood you dont have catfish, so a treatment dose of salt is a good plan, Ive also had good results with painting on malachite green based meds on the affected part with a model paintbrush (washed well!!). Dilute the med in a small glass of water first.
If it is fungus, it should lose shape and become less distinct when the fish is out of the water, its only fluffy when in the tank.
Fungus will usually apear when the skin/scales of a fish are damaged by another disease or from physical injury, so I wouldnt just treat the fungus as there could be a far more deadly underlying cause. You said the fish are acting funny, can you describe the behaviour as when my fish have had fungus, they usually act as normal.
Ken
