Hi, I had ordered for this 100 gal tank a 300w Schego Titanium heater but there is a problem with supply so only 250w or 600w available. So optoins were either 2x250 or 1x600. I went for the 600w, thinking that these heaters are supposed to be as reliable as it gets I din't need the redundancy of having 2 heaters in the tank and the extra juice may help if I need to bump up the temperature. I am happy with the setup I have in other tanks with an STC 1000 and an Inkbird 308 for extra safety (and the audible allarms)