This means the water should be circulated through the power filter a certain number of times per hour. It is recommended that the aquarium water be circulated through the power filter three to five times per hour. For example, if you have a 20-gallon aquarium, you'll need a power filter that circulates up to 100 gallons per hour. For a 55-gallon aquarium, a power filter that circulates up to 300 gallons per hour would work best. Most power filters are sold with at least one filter cartridge included.
Some cartridges are reusable.
If you buy a filter that has reusable cartridges, be sure to rinse the cartridge in some of your aquarium water or in dechlorinated water. Chlorine will kill the beneficial bacteria that have developed on the filter cartridge. We suggest that the filter cartridge or media be changed at least every three to five weeks depending on the fish load and type of fish you are keeping. Whenever you replace a filter cartridge , always rinse the filter cartridge before you put it in the power filter. If you don't do this, you'll have a black cloud of residue from the charcoal powder in the filter cartridge.