AquaMedic produce very high output titanium heaters for use with digital controllers, or if you are using a sump tank Jager (Eheim) 300w Heater/Stats are very efiecne tas they are rated to heat 600-1000 litres. I would personally "stage" heat, take your total wattage required (depending on aquarium net volume and potential for ambient room temerature fluctuation) and divide by 3. So if you say require 750w I would use 3 x 250w heater/stats,
if one fails in the on position the other 2 shall detect the rising temp and stay OFF, preventing them being boiled, if one fails in the off position, the other 2 shall stay on and prevent the water from becoming extremely chilled. This way both extremes can be avoided, unless all 3 failed simultaneously on or off, extremely unlikely. Remember equipment will fail at some time, even the most expensive kit, as any fishkeeper of long standing can confirm.
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