There are three types of filtration:

Biological – Biological filtration aids in the creation of beneficial bacteria which convert ammonia, a byproduct of fish waste and left over food, into nitrites and nitrates. Not all bacteria are harmful. Some bacteria take ammonia and convert it into nitrites. Other bacteria will take the nitrites and convert them into nitrates which are beneficial to the health of your vs. Chemical – Chemical filtration simply means absorbing chemicals and purifying the water. This is water purification, plain and simple. Mechanical – The filter captures debris and other solid particles as water passes through it.

Types of Filters:

Sponge filter – The most basic type of filter consisting of a simple sponge through which water is drawn by rising air bubbles from an air pump. The sponge initially acts as a mechanical filter and once matured can act as a biological filter. This type is ideal for small breeding and rearing tanks.

– The most basic type of filter consisting of a simple sponge through which water is drawn by rising air bubbles from an air pump. The sponge initially acts as a mechanical filter and once matured can act as a biological filter. This type is ideal for small breeding and rearing tanks. Box filter – This type comes in a number of sizes to suit small to medium sized tanks. The airflow draws water through the filter chamber that can be filled with desired media, such as wool, carbon or specialized adsorbent resins.

– This type comes in a number of sizes to suit small to medium sized tanks. The airflow draws water through the filter chamber that can be filled with desired media, such as wool, carbon or specialized adsorbent resins. Internal power filter – This type uses an electrically powered centrifugal pump to draw water through the filter material, usually sponge. Additional chambers maybe present for adsorptive media or additional mechanical/biological media. They can provide useful extra mechanical filtration when used together with undergravel filtration.

– This type uses an electrically powered centrifugal pump to draw water through the filter material, usually sponge. Additional chambers maybe present for adsorptive media or additional mechanical/biological media. They can provide useful extra mechanical filtration when used together with undergravel filtration. HOT/HOB filters – Hang-On-Tank or Hang-On-Back filters are similar to internal power filters in terms of design and the size of tanks where you can use them. Some models use disposable cartridge system to facilitate easier maintenance.

– Hang-On-Tank or Hang-On-Back filters are similar to internal power filters in terms of design and the size of tanks where you can use them. Some models use disposable cartridge system to facilitate easier maintenance. External canister filter - works on the same principle as internal power filters but are located outside the tank and draw water into the filter through an inlet tube and return the water via another tube.

- works on the same principle as internal power filters but are located outside the tank and draw water into the filter through an inlet tube and return the water via another tube. Undergravel filters (UGF) - works by drawing water from the tank down through the gravel substrate. It acts as both mechanical and biological filtration media. The gravel needs to be vacuumed occasionally however, to prevent the buildup of excess dirt in the gravel.

- works by drawing water from the tank down through the gravel substrate. It acts as both mechanical and biological filtration media. The gravel needs to be vacuumed occasionally however, to prevent the buildup of excess dirt in the gravel. Sump filters - These are usually home-made large outside filters placed below the main tank. These may include a smaller tank or other container filled with filter media. Heaters may also be placed in this sump pump.

- These are usually home-made large outside filters placed below the main tank. These may include a smaller tank or other container filled with filter media. Heaters may also be placed in this sump pump. Trickle (wet/dry) filters – These may also be home made but there are commercial models available. These filters are very efficient as biological filters and work similar to many sewage treatment plants.

– These may also be home made but there are commercial models available. These filters are very efficient as biological filters and work similar to many sewage treatment plants. Fluidised bed filters – These are specialized biological filters which rely on a constantly moving bed of sand as the filter medium. They act only as biological filters and require a mechanical pre-filter.

– These are specialized biological filters which rely on a constantly moving bed of sand as the filter medium. They act only as biological filters and require a mechanical pre-filter. Diatom filters – Often used for short term mechanical filtration to improve the quality of water in the tank. The filter media can clog easily because it traps smaller and smaller particles. You need to clean them after each use but are very efficient in giving the water a quick cleansing.

There are many types of filters on the market. It is an excellent idea to choose a filter that performs all the three filtration functions. Again, your local pet store can give you recommendation as to the type of filter you need depending on the size of your fish tank.