heaters are very strange, especially alot of glass ones lol. Be sure to watch the temp, i would set mine at 75, and it came on.... my temp would be 78. if I set it to 78, my temp spiked over 85. Its now set to as far down as it goes, and I bought another a dif heater. I got 2 visutherms, they were cheap, but 1 in my FW tank, temp never leaves 75. ones in my 55, temp goes from 80.9-79-5 daily.
Thank god I was fishless when I was using the glass heater.