Metal poisoning

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Metal poisoning is the accidental use of metals in the aquarium, leading to harm to its occupants.

The most common metals are iron, lead and copper, though others can harm, like aluminium, antimony, arsenic, bismuth, cadmium, chromium, cobalt, copper, lead, mercury, silver, zinc and tin, or alloys like brass and bronze.


Acute poison - leading quickly to death

  • Gasping at the surface or lying on the substrate
  • Shimmering
  • Uncontrolled swimming
  • Glazed or eyes not moving look

Chronic poisoning - Slow death

  • Loss of appetite
  • Breathing more rapidly
  • Shimmering
  • More likely to catch fungus and bacterial disease due to damaged immune system
  • Growth deformities


  • Metallic salts introduced into the water via tap water from your supplier.
  • Metals (especially copper) dissolving from the pipework in your tap water, especially if its acidic (pH <7) or hot.
  • Copper in medications. If dosing with copper based medications then know that some species of fish (like minnows) will be more sensitive than others. Shrimp and invertebrates usually die in the presence of even low levels of copper.
  • Metal ore in the rocks you've added to the tank.
  • Metal in the frame of the tank or in a piece of equipment.


  • Test for metals in the tap water and the tank water. You can buy test kits that measure iron or copper levels. Ask your tap water supplier if they add metals to the water. Ask them for a water report. This will have metals levels in it.
  • TIP: Turn on your hot water and cold water taps for several minutes so that old standing water in the pipes is flushed away before you use it. If the pipes still test for copper then it's probably in the water at its source. These metals may be harmful to your health, too.
  • Remove the rocks, shine a bright light on them and turn them slowly while staring at them closely. You are looking for metallic glints. To test, place rock in a container with fresh water and leave for a couple of days and retest for presence of metals.
  • If your tank water is acidic then any lead weights you have left in the substrate could be dissolving. Find and remove them. Note, many so called lead weights are in fact made of zinc.
  • Look out for bare metal in the hood that may be dripping dissolved metals as condensation.
  • The easiest way to remove metals is to do a water change. However, if the metals are in the water source, then you need a detoxing metal conditioner treatment.
  • Add a commercial water conditioner bottle that says it de-toxifies (metal-chelating) metals, typically using chemicals like EDTA.
  • Add a foam or resin that removes metals when water is passed through it. Typical foam like Poly-Filter. Activated Carbon is not good at absorbing metals.