Activated carbon for aquariums will help remove the residual copper in the water column (the more carbon you use the more it can absorb, and have to change it out more often for better efficiency), but the copper not in the water column would still be present.
Other than the tank silicone... do you have any rocks, wood or substrate in the tank? And bio-media in the filter? Those items will also retain and slowly release traces of the copper back into the aquarium for a while too... just need to do alot of water changes to gradually dilute it.
Using RO/DI water might help to lower the copper levels abit faster (compared to using tap water which in itself may contain certain amounts of copper too, especially in buildings with older pipings).
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