i'm so sorry for your loss. we almost had a situation like that earlier this week, the way our Eric's tank is made, there's a notch in the top for the filter to poke through, but normally it takes up nearly the entire hole. that evening, however, the filter slid down into the tank during a water change, and before we noticed it had slid we heard a loud flapping sound from his tank and saw him clear an inch of air outside the top before falling back in. now we're paranoid and have old betta-seller cups covering the notch, the feeding hole, and even the tiny notch for the airline tube to come out of.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)