Recently set up a 40 gallon reef tank in my garage. Since it's the winter and normally colder than the tank, I got 2 100w heaters and 1 200w heater just to keep it stable throughout the day.
My problem is that during the night, the temperature slowly decreases to around 68-70 degrees. Normally the tank is at 78 degrees.
How can I try and stop/prevent as much heat loss as possible from the tank during the night? I don't have any room to cram more heaters.