Copper does oxidize by water and a blue-green tint is the result. You'd be in great shape for warding off parasites and I believe things like snails. I would consider getting plastic, though.

Copper is used as a 'medication' for parasites such as ich, because in small amounts it kills invertebrates, such as the snails and parasites. However, it's not good for the fish either, copper can cause fish to go into kidney failure, so in time it could lead to premature death in fish. Larger amounts of course will kill them more quickly. Better to go with the plastic.

Karen