03-11-2010, 03:21 PM
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Copper is a heavy metal and all heavy metals are highly toxic to all organisms. The level of the toxicity varies, but it does not take much. As an obvious example, copper-based medications for ich always recommend half dose with sensitive fish; and they contain copper simply because copper kills the parasite.
In scientific studies, the only heavy metal more toxic to fish than copper is mercury. For plants, it is mercury, then lead, then copper. There is probably copper in your tap water (most of us have copper water pipes and the copper does leech into the water), which is why we use a water conditioner that detoxifies heavy metals.
Levels of copper safe for fish are much lower than for humans, so the adage that if we can safely drink it the fish will be OK is inaccurate. The safe level of copper for fish is 65 times lower than for humans. Fish show stress with copper levels of .02 ppm, whereas humans are said to be OK with 1.3 ppm of copper in our drinking water.
Nothing containing exposed metals should ever be placed inside an aquarium with fish and plants.