lucky to have a backup heater

[Motorfranco]

when I got home tonight,noticed all the nems not doing well,temp dropped to 74,I have 2 heaters in the tank,this shouldn't happen.then I recalled I unpluged one of then to rearrange all the plugs and forget to put it back on,and somehow the second was not plugged good enough and it's not function.
I am so lucky,tank could have crashed 1-2 days ago.