What's the dumbest thing you've done?

[MoeReefer]

woke up one morning at about 4 am and decided for some reason to do a water change. Just after i finished adding the replacement water i realized it was from the wrong buckett. 5g of fresh water makes a big difference in salinity when added to a 30 g tank. spent the next hour adding salt to the tank untill proper salinity was reached.