Are they sulfur based removers? Some of those heavy metal removers aren't too safe. I would keep adding until it stops turning black, as the reaction is believe is copper + sulfur --> copper sulfide (black)
When they stop turning black that means there is no copper, so I would keep going until they stop doing so. After that you should be fine.
Display tank - 24g nano w/ softies/montipora
I run electrical appliances underwater and enjoy injecting things with Kalk filled syringes.