After hearing all the concepts of one heater vs. two… I use one heater whenever possible… I won’t rehash the pros and cons to each here…
I have a 250 W heater in my 125 gal tank and the temp stays very consistent. And that’s with my fiancé turning down the air conditioning every time I turn my back… She would keep the house at 60* if I let her get away with it…
So are you saying there isn’t enough room for a standard sized 250~300 W heater in your sump? Not even on an angle? Looking at the pic it seems one should fit, but that could just be an optical illusion.
…and to echo Dan… That is one beautiful tank you have there…