Unfortunately today I killed one of my Tetras. I forgot to put a cap on HOB filter and it sucked inside. When I found this, fish was already weak, and one of the fins ripped out. Fish died couple of hours later in hospital bucket.
I'm so sorry! Don't beat yourself up too much. This could happen to any of us and your fish could have chosen not to swim in there. It's my water change day and I'm going to go double check that I put all the intake covers back right now!
You'll never make the same mistake twice! I now obsessively look under every lid that I take off an aquarium. I had a really healthy 6" bristlenose pleco hitchhike, dry out, and die before I found him. As pet keepers, we do the best we can and learn from our mistakes.