Copper is very potent stuff. I have had aquariums that were treated with copper sulphate in the past and were eventually broken down and put in storage then set up again. I had trouble keeping marine snails and some other inverts alive,even after a thorough rinsing/cleaning before setting back up.When i checked the copper level,after checking all other possibilities,i found a moderate copper level still existed in aquarium. Replacing silicone would probably be the way to rid aquarium of copper because i think this is where the copper is hiding ! However,it would be much easier/safer to just replace aquarium imo! Good luck.