As external filters sumps are larger than internal filters. They have more filter media inside which results in less frequent cleansing than internal filters and are more versatile with various specialist filter media available to improve the water quality and keep fish healthy.
External filters are usually more expensive than internal filters but will be worth paying the extra money for versatility and greater filtering capacity.
As the external filter has a big filtering capacity, the chambers of the filter can be easily adjusted to suit the tank conditions, for example, a larger coarse section for large messy fish like goldfish or specialist media such as Mountain Tree Filter Brush to greatly improve your water condition.
External filters sumps usually fit into the cabinet under the aquarium connected by two tubes. Water is pumped from one end of the aquarium, filtered and then returned back to the other end of the aquarium via a spray bar or other spray nozzles.
Filtering the water in an external filter is achieved through various chambers.
The first is the coarse mechanical cleaning which removes the larger particles, fish manure and waste fish food,
The second is biological which cleans the water of harmful ammonia, nitrate and nitrite and
The third is the polishing which removes the very fine particles.
Finally there is the UV sterilizing, which kills all pathogenic leads to fish diseases from the water.
Many of the new external filters now have a self-priming mechanism which allows water to be drawn from the aquarium into the filter ready to be pumped back into the aquarium. This device makes life easier when cleaning or servicing the filter.
External systems sumps do have some disadvantages: set up is a bit more technical with suction and discharge tubes going outside the tank, manual start-up is a bit trickier, and a more substantial budget is required.