Aquarium Filters: Most filters are divided into three sections: Biological, Mechanical and Chemical. 

Biological:

An aquarium filter is a breeding ground for two main types of good and essential bacteria. The main purpose

of these two bacteria is to break down ammonia and nitrite. 

Mechanical: The filters will also remove large particles of debris and other floating wastes.  

Chemical: Some filters have a place to add active carbon in order to remove medication from water, to clear

water and to remove heavy metal from water. 

The types of filers available: hang on filters, internal filters, canister filters, external filters, under gravel

filters and sumps.   

Internal filter: 

These filters come in a range of sizes and shapes to suit most small to medium sizes tanks. An internal

filter is designed to sit in the rear corner of the aquarium with the outlet just below the water surface.

Some tanks come with built in internal filters. The filter works through an impeller drawing the water through

the filter media forcing it back into the tank. The filter media can be sponge contains bacteria which convert

ammonia into nitrite and nitrite into nitrate. Internal filters are very easy to clean and easy to maintain. It is

also not expensive and easy to install. The physical size of the internal filter can be issue if you want to

hide it away. It is also must be cleaned regularly so after wile it became bother. 

External filters: 

External filters usually provide a good water cleaning and chemical values control. External filters sit

outside the tank. These filters have a huge advantage; they can contain more media inside them than

internal filters, so they tend not to need cleaning quite as often. To be accurate these filters need to

be taking care of every 4-6 month.  

Photo by: Killer

Canister Filters: 

Aquarium Canister Filters can be used in freshwater or saltwater aquariums. Internal filters come in a range

of sizes and shapes. It is a large and powerful filter. The recommendation for this type of filter is that it

should be large enough to circulate ten times the volume of water per hour. Canister filter work by the same

basic functions, water enters the filter through the lid which holds a magnetic impeller motor. The water

passes through large foam pads designed to trap floats. It then follows a route through a series of chambers

filled with various filter media (such as carbon or even sponge) that purifies the water. Finally the water

passes through another media. It is time the purified water to return to the tank.Canister filters

becoming more common these days. 

Undergravel Filter: 

Maybe the cheapest and simplest filter to maintain. The Undergravel filter draws water down through the

gravel across the bottom of the tank through small slots in the tray and forces the cleaned water back

to the top through pipes in the corner of the tank using power head (air stone is an option too).

The suction created pulls water and wastes into the gravel and provides a source of oxygen water for the

bacteria, which remove the resulting toxics from the water. It will also remove heavy metals and

medication from the water.