Ok, I confess. I'm a killer.
My fishroom runs with a water circulation system, trickle filter, sump etc.
Being the smart guy I am I decided to put an overflow in the sump, connected to the drain. For a water change all I need to do is connect a hose to the tap, run it to the sump and turn the tap on. After about 5-10 minutes I calculated I should have changed about 10-20%. Works great!
One Monday not too long ago my wife complained about hearing water running and that had been liked that since Saturday.(She could have told me earlier :roll: ).
You guessed it. I forgot to turn the tap off and was 'too busy' to check all weekend. Tanks where all about 10 oC with a full dose of chlorine and a lot off dead fish. :-(
This was worse than the flooding caused by a similar mistake a few years ago.