COPPER IS A BAD IDEA.....Just in general. You probably will not get totally rid of them without breaking down the entire tank and cleaning it with a mild bleach solution. If the snails seem to have just exploded then you are overfeeding the tank. the plecs and the tetras can be fed every other day-like Jinkzd said
and they will be fine, this will greatly reduce the numbers. Try that first, remember it will take a while for you to notice less numbers. If you want to try a more aggressive method and do not have any labryinth fish in the tank you can add any product to kill algae. For some reason it kills the snails, I think it erodes their shells or something.
