Look after the water and the fish will look after themselves (Unknown).

The adage above says a great deal about the importance of water quality to the health, vitality and general well-being of our fish. Although obviously simplistic, the message is very true, if we maintain excellent water quality for our fish we will find that they are healthy, grow fast, reproduce readily and utilise their feed efficiently. Sounds easy, so how do we maintain excellent water quality?

The first component of the water quality maintenance kit is the mechanical filter, also known as a particulate filter. This unit serves to remove solid particles from the water as quickly as possible. Particles that are not removed leech ammonia into the water, are colonised by bacteria and increase the demand on oxygen in the system, and can directly irritate the gills of the fish. Furthermore, such particles will block the biofilter and, if allowed to settle and accumulate, will rot and release hydrogen sulphide into the water, which is deadly to fish even at low concentrations. Mechanical filters generally only remove particles down to a diameter of about 30?m, i.e. 0.03mm. If your fish are very sensitive you may wish to remove these fine particles as well and the best method of achieving this is by means of a foam fractionator or protein skimmer.

Having removed the solid particles we next need to deal with the dissolved organics in the water. Ammonia is produced by the fish during the digestion of their feed and this ammonia is released into the water via the gills. Fish are sensitive to low levels of ammonia and it must therefore be removed by means of a biological filter, or biofilter. Bacteria (good bacteria!) live on the surfaces of the biofilter media. They feed on the ammonia and excrete nitrate (ultimately via nitrite) which is not very poisonous to fish. Nitrate accumulation is avoided by water changes.

During respiration fish use oxygen and return carbon dioxide to the water. The oxygen must therefore be replenished via aeration or even oxygenation in extreme cases, and the carbon dioxide removed by aeration.

In a properly designed system where these components are appropriately scaled according to the needs of the fish and suitably maintained, we will have excellent water quality. And we all know that if we look after the water the fish will look after themselves.