A reefer can not underestimate the importance of saltwater aquarium heating to coral, fish and invertebrates. All reef inhabitants originate from warmer seas and in order to accommodate them we have to ensure their needs are met accordingly.
Unfortunately, heaters can (and do!) fail and I’m talking from experience. Depending on the size of your tank, loss in temperature could happen over a few hours or within an hour and could prove catastrophic. You may have left for work in the morning and come back to a failed heater and water several degrees colder than it should be.
A heater’s thermostat could also fail resulting in much higher temperatures. Higher temperatures are actually worse for a reef than cooler temperatures. With cooler temperatures, processes that happen within coral slow down but the opposite occurs in higher temperatures. The latter causing permanent damage that some coral may not recover from.
Luckily there are steps you can take to help minimise this risk, all of which I discuss in further detail below.