sounds like you shoudl be god with the rock
now regardign the
copper.. better safe than sorry is the best way to go.
now honestly, if its an acrylic tank, then you shoudl be ok, but the problem is in glass tanks in that
copper tends to be absorbed into the silicone seams.
now i cant say for sur eif you will have an issue, that will be alot of water, so it shoudl be diluted greatly, and will likely not cause any issues. but i cant be sure. the glas wont absorb it (as far as i know) but the safe thing to do would be have the seams redone. im not saying that is required, but its the "safe" thing to do.
i have never experimented with this, but have heard peopel having issues. not sure what the times frames were though..
i wan tto make sure its clear, i am not speaking from experince, just from what i have read from others. most peopel are very adimat on the issue. but i cant say for sure whether you would be safe, or not...
its alos likely that a regular coper test wont show any readings, so if it comes up negative, it still may not be a 100% safe.
i would suggest soem more research, and make sur eany feedback ou get is from peopel with first hand experince, try to avoid, 2 hand stories, and hear say...