Aquarium filters provide the very important role of removing toxins and chemicals from the water. This is vitally important for the well being of the fish. A good fish tank filter will provide three important types of filtration. They are biological filtration, chemical filtration and mechanical filtration. To maintain a healthy environment in a fish tank all three of these types of filtration need to be met.
There are several different types of filters to choose from and each has it pros and cons. Most filters today will provide an adequate job with all three types of filtration. You can use power filters, which hang on the outside of the tank, canister filters which are also outside of the aquarium, and undergravel filters which use the gravel for filter media. Powerheads can be used with ungravel filters to improve performance of the filter.
When deciding which filter to buy you should consider what fish will be kept in your tank. Power filters do a great job but small fish or baby fish can be sucked into the filter intake. Canister filters are more expensive but there is no problem with sucking baby fish into the intake. Undergravel filters have a bad reputation of not doing the best job of filtering but with the addition of a powerhead their performance can be improved.
