Mechanical filtration is simply using filter media to remove waste debris from the water. Water is drawn up into the filter through the filter intake tube and is pushed through media such as filter floss, sponges, and filter cartridges. Debris such as fish poop or left over fish food will be removed and the water will flow back into your tank much cleaner.
To maintain a successful home aquarium, most agree to purchase an aquarium filter that turns the water over 8-10 times per hour. This means that if you have a 20-gallon fish tank, you want a filter that is rated between 160-200 GPH (Gallons per Hour). This means that your water will flow through the filter and around 10 times in an hour therefore more loose particles of waste will be removed much faster.
Please read Mechanical Filter Media to ensure you select the most appropriate filter media for your mechanical filter.