Heaters, though in some parts of the country a necessity, can be a dangerous piece of equipment. They can fail in the “On” position and heat up your aquarium dramatically. A couple of ways to reduce risks include putting the heater on a timer and even using multiple smaller heaters. If you put the heater on a timer, you can control the amount of time the heater is running. If a heater is only allowed to operate in 15-minute intervals, there’s less chance your aquarium will overheat. If you use multiple smaller heaters and one happens to fail, it’s small size will cause a less severe impact on the water temperature.