Filtration is key to having a biologically sound aquarium. You can never have too much filtration; the more you have the better your water quality will be. Filters provide a foundation for bacteria and also mechanically filter your water too, removing any small sediment to increase the clarity of the aquarium. It is recommended that when starting a new aquarium to use a filter star and a water preparation/conditioner to remove elements found in tap water damaging to bacteria.
External Filters are the ultimate filtration available for aquariums. They normally sit underneath within the cabinet; however the position of this can be altered if needed. The external filter will have a pump within it that retrieves water from the aquarium, through the inlet pipe and into the canister through the filter media then back up to the tank via the return pipe. As external filters are positioned out of the aquarium water displacement is not a concern so most external filters have a larger collection of media that the internal equivalents, making them a better and larger filter. External filters are up to 3 times more effective than internal ones designed to filter the same volume and because of this require a lot less maintenance. The duration between cleaning can be up to 3 months at a time. Also when cleaning is carried out it is performed outside the aquarium so it will not stress the fish at all. Some of the larger external filters have available spare compartments for media so you can place in specific medias, substrates and supplements.
Internal Filters are the most popular system for aquariums. They consist of a powerhead pump with a connected canister. In most systems the canister usually sits below the pump. The pump forces water up through the canister through an array of filter media and out through a nozzle. Most models come with an option of using an induction system so that air can be dragged into the aquarium, providing oxygen for the fish. The filter is fitted inside and normally attached to the side wall so that water can be pumped across the full length of the aquarium resulting in better circulation. The sponges within the canister have to be rinsed out and replaced when necessary, normally every couple of week.
Undergravel Filters consist of 3 major parts, a filter plate that sits under the gravel, uplift tubes and a pump to operate them. The filter plate sits under the gravel with attached uplift tubes. The uplift tubes either have air stones inside them connected to an air pump or a powerhead pump. The pumps create uplift through the tubes and in turn produce a vacuum through the filter plate and gravel. All waste and sediment is then pulled down towards the bottom of the tank where bacteria colonises and biologically brakes down waste. By using an air pump to operate the filter it also adds oxygen to the water, producing a better environment for the fish. This system is an old design but still functions well and is often found on many smaller tanks and professional quarantine systems. Fortnightly partial water changes (around 25%) are necessary with the aid of gravel cleaner in order to remove excess waste and maintain good water quality.