you nuke the rock, and all of the micro critters can then render your tank toxic when the copper kills them all off. if you are having an illness issue, i suggest putting your live rock in a bin with a mixing pump for 8 weeks to kill off any ick and treat the tank with copper and give the fish pvc and clay pots to hide in. once you have treated with the copper for 6 weeks remove it with carbon and waterchanges, until it tests out at 0, then retest the copper in two weeks, if still 0, ad back the live rock.
good luck