Heater wattage for 2 heaters in sump

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For a 120g tank (waiting for tank to arrive and ordering all the parts I need).

To avoid overheating due to heater malfunction I thought I'd use two heaters of a lower wattage rather than 1 heater of higher wattage. The alternative is one heater and then buy a controller to avoid overheating.

Also I thought I'd try the Won heaters because Ebo-Jagr's are too big to fit in my sump.

Is two 200-Watt heaters OK, my other option is either two 250-watt heaters or two 300-Watt heaters. The idea is if one heater sticks "on" permanently I don't want it to overheat the tank by more than 5 degrees or so.

Other heat sources in the tank will be return pump (either quiet one or Velocity T4) and lights (432 watts T5 pendant).