Let's list all the things that can go wrong to your tank .

[Mr Cob]

NEW ONE....assume you have a 55g standard stand and canopy to find out that you do not....when "game day" arrives. Forced to implement.

OLD ONE....build a foam structure and forget that foam floats and also forget that you have a center brace and your foam structure won't fit now....lol!

[alexdmg]

Not clamping your hoses to your high flow water pump. Eventually they will get hard and could pop-off and spray your power strips.

[loans_n_fishes]

Shocking yourself when you stick your hand in the tank because one of your powerheads is leaking electrical current.

Losing ALL 15 of the baby seahorses you nursed to 10 weeks of age because of a sudden outbreak of hydroids! :( AND Finding medication for hydroid removal (Turns out it is GOAT dewormer! You should have seen the look on the feed store guy's face when I told him it was for seahorses.)

Getting bristle worm bristles all over your hand because you were too lazy to put on gloves to move rock around.

Having to stay home for days at a time to float frozen bottles of water every 1/2 hour in your seahorse tank because the AC goes out in the middle of summer---on a Holiday--and no one can come to work on it for a week. Apparently overheating an aquarium is not considered an "emergency".