In this thread post your most idiotic reefing mistake

[kengeroo]

got really lazy one day,,, added salt directly to my tank,,, straight into a clam.....

[shrimp]

Might as well post mine.
Years ago, I was doing a tank move and fished out all my fish to a 5 gallon pail. As the move was taking longer than expected, after some time I figured that the water must have cooled off too much, so I decided to place a heater to warm up the water a bit.
Even though I had the thermostat set to turn off when the water would heat up to the desired temperature, I "boiled" all my fish as I did not have a small circulating pump in the bucket.
It still pains me to think about those poor fish that day, even though it happened so many years ago

[fishoholic]

I was messing around in the sump and must of bumped the phosban reactor. Unfortunately I didn't realize I had and the hose came loose causing water from the sump to leak out onto the floor. Got home from work the next day to a soaked basement carpet. At first I thought the sump had cracked and was leaking until Doug found the hose disconnected.