Wow!

I would try a different plug. I wonder if they are shorting out or something. It seems odd that every heater you have gotten has done this. I use Ebo Jagers and have had the same heaters for 4 years now. I have 2 100 watters on my 270. My water gets plenty of radiant heat from the Halides but as I convert to LED's I will be looking into other options as well to maintain a temp of 79-81.