Originally Posted by intarsiabox (Post 621921)

2x150w or 2x200w should be fine. With higher wattage the heaters can heat up the water faster in a shorter time so will be on less but the smaller wattage one take longer but use less power so it's pretty much a wash. 180g of water doesn't lose it's heat instantly so a single heater will have no problem keeping up but have a second as a back up. Your controller has a low/high temp alarm I believe.