My Tank crash - Hopefully you can learn from my experience :(

[rsisvixen]

Originally Posted by ComfortablyNumb

A dark tank, as presumably the OP's tank was as the claimed outage happened at night, would also use up less o2 due to the relative inactivity of the fish.

While true fish might use less oxygen at night, a tank also has less dissolved oxygen at night with the lowest levels of dissolved oxygen just before lights on. All photosynthesis is halted without light, and algae and zooxanthellae will use up dissolved oxygen and release carbon dioxide at night.