I use two small heaters rather than one large one. The odds that both fail at the same time is pretty astronomical, and if only one fails on or off it won't change the temperature drastically.This gives me a good "bang for my buck" for the $ I forked out on the components of a second tank (which wasnt much). Plus It gives me a back up heater in that I can yank out and move to the display if I ever suspect any problems with my current 200W heater.