If you have an aquarium, then chances are you have a filter for it. The main purpose of aquarium filters is to filter out the ammonia produced by fish. The ammonia actually breaks down into nitrates which are very harmful to aquarium fish.
There are various types of aquarium filters that you can choose from when finding one for your tank. One type is a corner tank filter. This filter is a small black box that fits in the corner of your tank. It has slits in the bottom, on the lid, and on each side and a small pump that sucks the water up through the bottom of the box. The filter inside consists of two layers. One layer is made of activated charcoal which is in the bottom and allows the water to be filtered chemically. Above the charcoal there is a layer of polyester or cotton batting. This helps in the mechanical filtering of the water.
Under gravel aquarium filters are a great way to filter the water in your tank. An under gravel filter is meant only for biological filtration because the gravel is where most of the bacteria grows. There are pumps that suck the water up and redistribute it across the top of the tank. These are the most ineffective of all filters when used alone. They should only be used with another type of filter.
The hand on the tank type of filter is just another choice you will have among aquarium filters. This type of filter hangs on the back of the tank with a tube that comes out of the filter to suck water up to the filter. The water is pulled up into a black box that has physical as well as chemical barriers that the aquarium water flows through. Once it has flown through each barrier, it is pumped back into the aquarium. This is a very efficient filter to keep your tank clean.
When looking for the best aquarium filters, the canister filter is a great choice. It is an external filter with three various filtrations. The water is sucked out of the tank and into a canister where it runs through activated charcoal, a physical barrier, and a medium filter before being sent back into the tank. The canister filters tend to cost a bit more than other styles, but they are very easy to maintain and very effective in filtering the aquarium water.