Wow, I am really sorry to hear that you lost everything....
It definitely started because of the copper. To prevent this from happening, don't ever put copper into your main tank. Me personally, I never recommend copper use at all. It is too dangerous to many animals (tangs, angels, butterflies, lions, puffers - deadly to inverts, plants, rock).
Now, you are going to have to really work to get all the copper out of your tank..
I would be giving that LFS a piece of your mind. Did they even tell you the side effects of using copper, or ask you whether you had live rock or a quarantine tank to use the copper in? Did they ask you what fish you were treating (a copper sensitive puffer, with other HIGHLY copper sensitive fish)?