Temperature Worries

Happy Thanksgiving everyone! I am closely watching the temperature in the tank (currently 75.7). It should be at 78 degrees consistently. We keep our house pretty cold, so I have 2 in sump heaters (300 watts each, 2 in case one beaks) to help maintain the temperature at 78. There are 2 risks… if I set them up too high; the lights (which are very powerful) can make the temp go above 78. It has happened before. The corals pretty much start to die. Nice fish soup! If the temp goes below 76, I get worried as well and the corals also start to suffer. Different season in the year represent a challenge. I think the fall season is one of those since it is getting cold at night but is still a bit warm in the house during the day. I am about to go online and order 2 new heaters since mine are about 5 years old.