This is my back up. I will be switching out a cold water tank in the future and it will be in use full time. But for every tank should have a back up. These are great to add to your tank as you can dial in temperatures. I run two heaters per 55 or greater tank. That doesn’t have hot spots and cold spots in tank.If you have anything over 45 gal you need two and a back up. You put money in your fish don’t want to lose them because of half heated tank or one breaks down. Many fish need 80 degrees and a heater has to work twice as hard if you don’t have a large heater to handle it. Two is less wear and tear on a heater.