As soon as fish are added to an aquarium, the normal processes of respiration and digestion produce waste products that pollute the water. There are also other sources of pollution, such as decaying uneaten food.
The biggest challenge in keeping an aquarium is controlling the level of these pollutants so that your fish have a healthy environment. One of the things you need to meet that challenge is an effective aquarium filtration system.
In many ways, aquarium filtration is the most complicated and difficult aspect of fishkeeping. A visit to any well-stocked aquarium or pet store will reveal an astonishing array of filters that vary widely in design and price.
In addition, the beginning aquarist faces a lot of new terms that are used to describe filters. Understanding how filters work and what they accomplish can make it much easier to sort through everything.
You may assume that the basic goal of filtration is to remove debris floating in the water so that it doesn't cause pollution. While this is correct, it's only part of the story.
This process is mechanical filtration. If mechanical filtration is sufficient, very little solid matter will be left floating in the water. However, just because the water looks clean doesn't mean it is safe for fish.
Most of the pollution that causes the water quality to deteriorate can't be seen. In order to remove it, two other types of filtration are needed: chemical filtration and biological filtration.
Only when mechanical, chemical, and biological filtration are available can a truly healthy environment be maintained for the fish. Aquarists often use two different filters together in order to provide these three types of filtration. This is because filter designs that are very good at providing one or possibly two types of filtration tend to be less effective at providing the remaining types.
Go to the next section to learn more about mechanical filtration.