Things you have found out the hard way - aquarium related

[Invigor]

did you know wearing bare feet on a concrete floor in the basement is a good way to find out if there's stray voltage in your tank?

another one I learned that's pretty widely known now:

did you know when you're setting up plumbing from the return pump all it takes is a tiny hole to make life sooo simple. when you unplug your return pump to make sure your sump doesn't overfill from the dropoff water, you find out the water from the tank starts sucking through your return pipes, so in a panic you plug the pump back in only to have your overflow NOT work and have water pour over the lip of the tank. So while maintaining a certain water level in the tank by plugging and unplugging the pump with one hand, you only have one other hand to find a way to break the syphon from your extremely well glued PVC pipe and when you finally do get the syphon broke, you're scared to try it again.

did you know a 1600gph pump in a 5gal pail isn't a good idea to mix water with while you're on the way out the door late for work.