Heavy metals

What are they?

Heavy metals are chemical elements such as cadmium, copper, lead and zinc.

They dissolve readily in water and are dangerous to aquatic life in high values. In most countries there are health restrictions on the upper level of these metals in our tap or well water. But some fish, amphibians and invertebrates find even these metal levels highly toxic.

What do they do?

They get into an animal and damage its breathing, growth, waste control, brain and reproduction organs. Usually killing it eventually.

• Once these metals get into an animal, the metal can not be removed and the levels can slowly build up over time.

• See Metal Poisoning disease.

How does it get into the water?

Some water bodies are contaminated with significant amounts of heavy metals. Industrial mining is a major source of heavy metal contamination of water supplies. Being "pure" elements (rather than complex compounds that ultimately break down), heavy metals may continue to pollute watercourses for years or decades.

Apart from the water supply, there are other routes by which heavy metals can enter the aquarium. Lead, zinc and copper, for example, may leach from old pipes or galvanised or copper water pipes.

Heavy metals may also be present in certain types of rock - something to bear in mind if you are thinking of collecting rocks from the countryside to furnish your tank.

How to get rid of them

You can buy chemical sponges that will remove some metals as the water is passed through them.

• Products like Polyfilter or resin-based water purifiers can remove these metals.

• Activated carbon has limited use and can only remove small amounts of some but not all toxic metals.

• Use a chelating agent. This is by far the most popular method by the majority of aquarium owners.

You can neutralise the metals by chelating them. This is a chemical (usually dissolved in water) which you add to an aquarium and converts the metals into a non-toxic version.

There are several liquid products you can add to your aquarium water that render the toxic metals non-toxic for a period of time. Some water conditioners have a chelating chemical for example.

Currently the best ones on the market are Prime by Seachem or Rid Metals by Kordon. But there are lots of alternatives available.