Now where did they go?
I've been working with a 72g bowfront that is a community based tank, and two of my neons disappeared with no explanation the same way. The strange thing is that they were two healthy ones. I mean there's one in there that is having trouble swimming and would have been a good target, but he's still alive. I figred the two may have died from stress or other causes and the tankmates cleaned them up. I know that the other tetras and the bala cleaned up one platy really quickly. So, I would agree with most of what's been put here, that they died and the clean up crew kicked in.