stupidist thing to date was balancing on the arm of my settee (couch) so i could reach the clean water pump in my aqua-medic percula 120, these tanks require the arms of an urangutan to maintain the pumps, however the settee shifted just as was about to retrieve the pump ,and to stop myself falling into the tank i instinctively grabbed the metal halide pendant the steel suspension wires gve way and the M/H pendant ended up in the tank fizzing and buzzing, i cut off power supply quick as i could and luckily never had any livestock suffer, lights were ruined.
My wife still says i wrecked lights on purpose so i could upgrade to arcadia series 4 pendant.
Another stupid thing i done was to move my 6 inch maxima clam off the sand bed due to blue cheek goby constantly dropping sand onto mantle not thinking i placed it on rocks directly above pump oulet , a few weeks later i forgot to check flow into sump the which ran dry resulting in the pump blowing out millions of air bubbles straight onto the clams mantle, unfortunately clam died and i keep the shell to remind me how stupid i was. unfortunately reef keeping mistakes often not only result in some loss of livestock but are more than often very expensive ones.