I see no one else replied, but the answer is very simple (for anyone else who can learn from this): Discus cannot tolerate the same bacteria or parasites as many other aquarium fish. They aren't equipped for it, because they evolved in tannin-filled waters. If you put them in a tank with any other species, you're rolling the dice. It may turn out okay, but it may end in disaster. I'm truly sorry for the experience you had to go through - I learned this the hard way also.