Sources of Heavy Metals in Aquariums and How to Prevent Them

Aquarium metal contamination comes from plumbing, well water, metal hardware and copper medications. Learn the sources and how to prevent each from poisoning your tank.

Heavy metals rarely appear by magic; they enter the tank from identifiable sources. Knowing where contamination comes from lets you prevent almost all of it. The three big categories are the source water, objects placed in the tank, and treatments added to it.

Source water and plumbing

Tap water picks up metals on its way to your tap. Copper and lead leach from household plumbing, brass fittings and old lead-containing pipework, and the leaching is worse in hot water and in the first water drawn after the tap has stood overnight, because standing water has more contact time with the metal. Brass deliberately contains some lead for machinability, which can elute into the water. Even the municipal supply can carry low levels of metals before it reaches the house. Well water is a different case: it usually has no chlorine, but it brings metals straight from the ground, commonly iron and manganese, and sometimes others, so it should be tested rather than assumed clean.

Objects in the tank

Galvanised (zinc-coated) and brass hardware, and stainless steel that is not aquarium-grade
Lead plant weights and old lead-strip plant anchors
Painted, metal-containing or non-inert ornaments, and coins
Untested rocks, clay or laterite that may carry metal content
Cheap gadgets or batteries that can leak into the water

Treatments and additives

Copper-based medications and algaecides are an intentional but easily forgotten source. They are effective against parasites and algae but lethal to invertebrates, and copper from them lingers in the system long after the visible problem is gone. Never dose copper in a display, shrimp or reef tank; treat in a separate hospital tank instead. The same caution applies to any general medication: check the label for copper before adding it to a tank that holds shrimp, snails or other inverts.

Prevention checklist

Test your source water (tap or well) so you know what is in it.
Run cold and flush the line before filling or doing water changes.
Use only inert, aquarium-safe rock, decor and equipment.
Choose lead-free plant weights.
Keep copper medications out of display and invertebrate tanks, and quarantine treatments elsewhere.