Unfortunately your story is not too unusual. Did you do a water change after they died? There is a lot of chemical interactions that occur between reef animals that we just don't know or understand. Mushrooms are bad about chemical warfare with their own kind. I remember one time I had some real nice shrooms and when I added a different kind, on the other side of the tank the others quickly died off. There was no problems with water levels and everything else in tank did fine.

So sometimes you are not going to figure it out. Look this is a great segway to tell your wife you need a bigger tank (have to look for the positives in these kind of things.) More water volume means less chance these chemical interactions will have a deadly affect. At least that sounds like a good reason.

Good luck and keep the faith.

Mike