Not that big a deal, copper will bind to rock and sand and glass but does break down over time and running chemi pure or poly pads for copper will reduce what is released. There are some methods for cleaning up glass that involved very nasty acids and solvents but I would avoid these as it is an accident waiting to happen. Scrub really well and rinse many times with ro/di water, don't reuse rock and sand, equipment should be cleaned really well and the chemi pure and pads installed, if your labour is cheap maybe this is ok, personally if its a used tank AND its had copper I would just shine it on lol