Well, I set up a 44 gal. Brute to hold fresh RO/DI water above the 32 gal. trash can I already had for mixing saltwater. I was cleaning out my frag tank which had gotten covered with algae and used up the mixed water in the 32. I opened the valve to fill it back up and the kids started acting up so I got distracted and went into the other room to tell them to stop. I went back to working on the frag tank and completely forgot about it. Luckily it is in an unfinished section of the basement and I was able to vacuum it up with a shop vac.
The "kids acting up factor" That has gotten me a few times. They especially love to do it when I am shoulder deep in the tank trying to glue a frag on or something.