I was using the 500 watt version of the hygger heater for my mixing tank. I forgot to check the water level one week and my auto water change system had drained the tank to bottom exposing the heater. The heater is supposed to shut off when exposed to air but it did not. I started hearing an alarm on the heater controller and when I checked on the mixing station the heater had completley melted. The controller was showing HH and it was still cooking itself. Luckily I caught it in time that it didn’t melt my mixing station or catch on fire. I have since added an optical sensor to my mixing station to detect when the water level is low and turn off the auto water change system. I am using a different heater brand from now on.