Aquarium Filtration Overview

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.

Chemical Aquarium Filtration

Chemical aquarium filtration is needed because a number of dissolved, invisible compounds accumulate in aquarium water and they can't be removed by mechanical filtration. These compounds are not toxic to the fish but can inhibit their growth and cause chronic, low-level stress that eventually leads to disease. Most of these compounds are dissolved organic substances produced by natural biological decay.

The dissolved organic substances eventually reach concentrations high enough to become visible as a yellowish tinge in the water. You can see this when a sheet of white paper is held behind the tank so that half of it is viewed through the water. If the water is healthy for the fish, the paper viewed through the water will be as white as the other half; if not, the paper will have a yellowish cast to it.

Chemical filtration removes many, but not all, of these compounds. However, some substances that affect the growth of the fish can only be removed by making partial water changes on a regular basis. If this isn't done, the fish will never grow to normal adult size. This stunted growth will result in fish that never achieve the beauty of mature fish, and it can cause other related health problems.