That copper absorbs into the LR
(killing any invers, however small), sand and everything in there, possibly your equipment like your filter and such.
If you change your sand you will loose the bacteria bed in it and will need to cycle again.
Possibly the only way to get rid of copper completely, some one correct me if I'm wrong, is to strip the tank wash thoroughly and even strip the sealant and reseal the whole tank, and I'm not even sure if this would work on glass and acryillic.
Just read you other post about the pennies. How long have they been in there?