mysterious fish losses

[Aquamarina]

I did have the water tested again last week at a fish store with the same results I had, and they suggested the Marine-Max (which I added once), and also Cupramine (a copper formulation) which I did not add, not knowing what the problem was. The fish have appeared to be as usual, until one suddenly looks ill. The remaining fish currently are behaving normally and appear normal, while the butterfly in the quarantine tank is still alive, but upside down this morning.