There seems to be a huge issue here that nobody is talking about. IF you choose to do the acid bath it will clean your rock
BUT BE WARNED it will also
drastically weaken the rock (depending on the density, structure and the organism that created it).
IF I was going to do this I would use white vinegar, for two reasons:
1) it comes in a dilute easily available solution that cant harm your rock with a short bath
2) vinegar will have a similar effect as any other acid on calcium carbonate but the residue is not only non toxic but will feed bacteria capable of cycling your rock. white vinegar is acetic acid.
If you still feel uncomfortable with the copper situation run some copper resin on it for a week or so. that should do it.
FUN FACT: you can dissolve an egg in vinegar (try that before you dip your coral in HCl
)
Zar