What are reasons for major tank crashes?

[timdam]

Just starting a new tank. Would like to, of course, prevent any future tank crashes. What are some reasons why tanks crash? And how can it be avoided?

 

[Dmorty217]

The three main reason why tanks crash are... You go out of town and have someone lacking knowledge feeding your fish. 2. Sand bed gets stirred up and releases gases into aquarium. Heater fails without a controller frying your tank