I was checking my water and noticed that the heater in Benji's tank is broken. The glass at the bottom was completely broke off and the heater was flashing on and off. I removed it and threw it away but I also had 3 dead otos and one dead platy in the tank. BenjI and the other platy seem fine, but I'm worried that I shouldn't leave BenjI or Polly in the tank. I don't know where to put them though as I have no heater in my QT yet. Do I need to restart the entire tank after a through cleaning? Why would a broken heater kill my fish?