All aquariums require good filtration to keep the water clean and the fish and plants healthy. The most convenient type of filter for freshwater aquariums is a motorised external box filter, which hangs over the side or back of the fish tank. The filter uses a magnetised impeller to draw dirty water up through a siphon, forces the water through a filter media (such as activated charcoal and nylon floss), then pumps the cleaned and aerated water back into the tank. You will need to change the filter media when it becomes clogged with debris. Many aquarium suppliers offer charcoal and nylon floss in convenient pre-assembled pads, making filter replacement a snap.
Disconnect the power supply from the aquarium filter as well as pumps and heaters to avoid electric shock.
Lift out the old filter pad from the filter box. It will be full of water, so have a trash receptacle nearby and use old towels to clean up drips.
Discard the used filter.
Remove the new filter pad from its package and tap it gently inside the trash receptacle to shake off excess charcoal dust.
Slide the filter pad into place in the external filter.
Fill the filter box with water before turning the power back on (this is called priming the filter).
Turn power on to resume pumping water through the filter.