WOW that sucks, looks like a very agressive tank. Must have been impressive. What kind of filtration and how big is tank. I was also wondering what they ate last. Maybe something in food. I would also look into pest control. Sometimes they do not stay away from tanks with spray. Maybe some got into tank, just a thought. Again sorry for the loss, I lost 1 24" big aro and was sad.
(There needs to be a hug smiley for just such an occasion...) Why'd you rule out your other theory? I didn't think it sounded too bad...