X3...
Copper, sadly, will take more than two weeks to eradicate velvet from the tank. It's going to be a month - 30 days - and that's without ever once allowing it to slip below therapeutic levels. Not even for a few minutes during a water-change. Velvet's a tough son-of-a-gun, and you can't take chances with it.
You can use water changes, carbon, Poly-Filter, and CupriSorb to help remove it at the end of the one-month treatment, but as Melypr1985 mentioned, don't try to add any invertebrates until your copper test reads completely clear. (You might consider keeping a fresh Poly-Filter or CupriSorb packet in your system for a while, to catch any copper leaching from the rock or sand.)
~Bruce