Pennies in tank

[ChicoRaton]

Since 1982 pennies are made of 98 percent zinc and 2 percent copper. But heavy metals are not good for fish. Copper binds with blood cells. Very bad.

Not really important, but relevant:

The new pennies are zinc with a layer of copper over it. Take a pair of tin snips and cut a penny in half. You'll see it looks like a sandwich... So the metal contacting the water is still 100% copper, which is fairly bad for fish and VERY bad for invertebrates.