Author: Dr. L.E. Freese

Heavy metals are defined as metals that have a density of at least five times that of water. These include mercury, nickel, lead, arsenic, cadmium, aluminium, iron, platinum and copper. Metals such as iron, copper and zinc are necessary in small quantities for life. On the other hand mercury, lead, cadmium and others have no apparent metabolic function and are poisonous to humans, animals, fish and plants, and thus the term "heavy metals" often refers to the toxic heavy metals.

Heavy metals enter our tap water in different ways

• Lead and copper pipes as well as the solder used to join the pipes
• Brass chrome plated taps
• Air contamination
• Industry e.g. waste incineration plants
• Cigarettes

• Metals that are in contact with the water
• Ground water contamination

Heavy metals are toxic to fish if the accumulated levels get too high. The problem is that heavy metals not only accumulate in the aquarium or pond but they also accumulate in the tissues of the fish. In the organs of the fish they cause a variety of physiological problems which ultimately lead to disease and death.

Iron for example will cause an irritation of the gill tissue if the level is above 0.1mg/l. This irritation leads to gill tissue damage and this forms the perfect environment for secondary bacterial or fungal infections.

Firstly we must see that the tapwater has as little heavy metals as possible. To achieve this certain precautions must be taken when using tapwater.

• Let the water run for a little while before using it.
• Use only water from the cold tap as hot water increases the leaching of metals into the water
• Don’t use metal implements to transport water into your aquarium or pond
• Treat the tapwater with Anti-Chlorine which eliminates heavy metals

Secondly there are precautions that must be taken in the aquarium or pond itself

• Ensure that the equipment you use does not have metal parts that are in contact with the water
• Do not remove all the sediment at the bottom of the pond or aquarium, as the heavy metals react with the sediment and thus are in a non-toxic state
• Ensure that the water is adequately aerated, as oxygen binds with the heavy metals and in the oxidised state they are normally non-soluble and therefore safer