It almost happened to me with my pleco tank. Some adult in the house inadvertently switched off the power strip to the tank. I caught in time and only lost 3 small L114 plecos. I have more than a $1000 worth of plecos in that tank. I had to add a lot of ammonia remover to neutralize any ammonia that maybe in the tank. The plecos were gasping for air on top. That is how bad it got. I had an air pump for that tank but it was on the same power strip. I don't know how long it was off.