Jim, I really think it is toxic tank as well.
You had the bounce sheet thing, you mentioned something to me about painting in the house, and really just because you have burned scented candles in the past without effect, doesn't mean all of this didn't build up to the point where the fish just couldn't handle it any more.
BTW, there was a thread on the newsgroup years back about scented candles and their detriment over time.
Hopefully things will improve with water changes and carbon.