Unlike other animals that can regulate their own body temperature, fish have to entirely rely on their environment.
This resource page is dedicated to detailed information about any type of heater an aquarium may need. Learn about the different specifications and use cases for each aquarium heater.
5 Best Small Aquarium Heaters (Under 6.5″) for Nano Tanks
If a compact aquarium is what you want, then you need to carefully consider the size of its equipment.