What is a 'hang-on mechanical filter' for an aquarium?

What is a 'hang-on mechanical filter' for an aquarium?

Marc Grover (Professional Aquarist) gives expert video advice on: Generally, how do filters work in an aquarium?; What are the best filters for a small freshwater aquarium?; What are the best filters for a large aquarium? and more...

A hang on filter or a water fall filter is again, as the name implies, it usually hangs on the back of the tank. It has an uplift tube that drops down into the water and an impeller that is inside the filter mechanism that creates a suction. Water gets pulled or sucked up the uplift tube, and then pushed through the various stages of filtration media, in that hang on section, the compartment and then water falls back into the tank. So 1, 2 going up, water fall coming back out. And typically, the filtration stages are a carbon pack, and a sponge, and maybe another type of chemical resin that tries to eliminate ammonia, or what have you. And sometimes they work and sometimes they do not. That is basically what it is.