@DiscGolfRob
If you don't live in arizona, texas, new mexico, california, florida get a heater appropriately sized for your aquarium. His likely works undersized because it barely needs to turn on and when it does it's only a degree change.
With winter or fall/spring anywhere else in the country you will need a sufficient heater.
I bought 2 150 watt Eheim Jager for my 50 cube.
Instead of switching/cycling back and forth between both heaters like some do; I'm just going to use one fulltime and the other in there as backup in case the fulltime one fails.