I found them...

the missing fish were in the filter! The spongy bit on the filter had dropped off and the poor fish were sucked up the filter and were lodge in the spindly bit. That's why I couldn't find the carcasses. So it had nothing to do with the controlled environmental at all. BOOOOHOOOHOO! Nigel was decapitated. I'm not getting attached anymore. It's too emotional. I'm just going to get a cardinal tetra school so that I can't tell any of the fish apart. Of course, I say that now when I'm not at the fish shop.