The inline heater is another option that you can use to heat your tropical fish tank. This type of aquarium heater is actually installed on the outside of your aquarium. Inline heaters are used on tropical fish tanks that use canister filters or sumps. The inline heater installs in the middle of the return tubing off of your canister filter.
This allows for all of the water flowing out of your canister filter to flow through the filter and heating it as it flows from your canister filter or sump and back into your tropical fish tank.
The biggest benefit in using an an external heater such as this is that it is hidden from sight and takes up no room inside your aquarium tank.