Sorry for your loss
I am new at the saltwater tank ,however I was rasied in Fla. and started with saltwater fish. I had them for many years and never had problems maybe due to the fact that I changed tank with fresk ocean water every two weeks. I write this because now in Atl. I have to learn how to do it right. My one and last fish to be placed in my tank was to be a Flame Angel. I have had my tank set up for a year and all fish are healthy. So I purchased a Flame Angel only for it to do exactly what your fish did with in a week. I was hurt and felt the same as you. I pride myself on watching the water levels I have even been accused of making it a science and not a hobby. Well, I read as much as I could about a Flame Angel and bought another one. I could find no reason why the first one died. I lost the second one. Same way. This was heart breaking. I was helpless. After asking a endless number of questions I thought about something kind of strange. The best fish in my tank that have lived no matter what, Even when I had power loss for two days. Came from a fish store 40 miles from my house. The closest store which is always dirty and I find dead fish in there tanks from time to time is only 15 miles from my house. I have bought many fish from them and about 50% have survived. The ones I managed to save have grow very healthy. They were never very nice looking when I purchased them and I figure I was saving them from the stores lack of caring. Long story short I went back to the store 40 miles away a bought a third Angel. Tiger is just as happy as a pea in a pod. I have asked every question on what was it that killed the other two and can find no answers. I believe there must be a thousand reasons one would die. All we can do is try to make sure everything in the tank is in harmony and as perfect a place to live, then it will be up to nature. Hope you find another Angel and sorry you have to take a fish back. I have been through that too.
I keep trying and trying and trying. It can't be that hard.