Copper is basically poison and can cause internal damage, especially in angel fish. IMO this explains the high mortality of the more sensitive angels i.e. flames when purchased from copper treated holding tanks.
The symptoms are just as you indicated. Decrease in appetite followed by death. In the case of aquarium fish this death is also sometimes attributed to cyanide collection methods when in most cases its probably copper exposure.
Its not just fish either. If you google copper you will find a site detailing the liver failure in vineyard workers. The crop was traditionally sprayed with copper solution for the same reasons we use it in our hobby, parasites. Over the years the vineyard workers livers were destroyed in the process.
And yes; even the livers of those workers not drinking a gallon a day of there end product
There are some excellent authoritys here on the forum to detail a hypo treatment and or a sticky up top explaining just how to go about this. If I were in your situation I would start doing small water changes with fresh water to bring copper levels down and at the same time get started at reduceing salinity levels for a hypo treatment.
