Filter Dilemma 

Author: Dr. L.E. Freese

There are different filters available at various prices and it is advisable that the filter is not only bought for its affordability, but because it is suitable for the aquarium setup that you envision and that the maintenance that is required suits you.

 Firstly one must decide if you would prefer a motor driven, air driven or a trickle filter and should it be external, internal or undergravel? Each method of filtration has its pros and cons and these need to be weighed up before you purchase one and find that it does not suit your needs.

The capacity that is needed varies depending on the size of the aquarium and the waste load. The capacity of a filter is determined by the volume (of the filtration media) and the turnover rate (rate at which the water flows through the filter) of the filter in relation to the size of the aquarium and the amount of waste produced by the occupants. Excess volume does no harm, but if the volume of media is insufficient the filter clogs up very quickly and this leads to an increase in maintenance requirements. If the turnover rate is too high the turbulence in the aquarium increases and this leads to increased level s of stress in the fish. On the other hand cloudy water and insufficient filtration is the result of a turnover rate that is too low.

In container filters (canister, box or trickle) where no specific media is required, different media can be used depending on what type of filtration you require. There are 3 basic filtration methods and they have different media which are suited for these functions.

1)Biological – Media provides a home for the bacteria of the nitrogen cycle

2)      Chemical – Media reacts chemically with the elements in the water and thus changes the pH, salinity, hardness of the water or removes pollutants  

3)      Mechanical – Media removes suspended particles in the water and this ensures clarity


Calcium Carbonate – Hardens water and increases the pH of the water. This media can be washed and reused.

Carbon – Removes certain medications, heavy metals and chemical contaminants from the water by absorbing them and therefore it needs to be replaced frequently.

Zeolite – Neutralises ammonia through an ion exchange process and needs to be replaced and it should only be used as an emergency media not as a replacement for the biological breakdown of nitrates and nitrites in the water.  


Media that is used for mechanical filtration is most often used for biological filtration.

Ceramics – Porous and in various shapes which are generally used as biological media.

Filter wool/floss – Cheap and can be washed and reused. The problem with this media is that it tends to clog up quickly and needs to be washed fairly frequently.

Foam – A very efficient mechanical and biological filter media, which can be washed and reused. It can be bought in different porosities, which makes it more versatile than other media and water flow through the foam is uniform and thus a greater surface area is available to the bacteria. Make sure that the foam is filtration media, as mattress foam clogs quickly, is not easy to clean and may contain chemicals that are toxic to fish.

Gravel – It must be aquarium gravel and not sand (clogs easily). Washing is not so easy but it can be reused indefinitely.

This is only an overview of filtration and its media, it cannot be stressed enough how important it is to do a little homework and find the filtration system that will enhance your aquatic pleasure


September 2001