Rock and substrate can absorb copper, making accurate measuring of copper level impossible; THIS IS VITAL. Copper will kill all inverts, including coral and all algae (including desirable algae); possibly creating an ammonia problem. Copper can stay in the rock & substrate for who knows how long. It would be a long tome before I trusted an anemone, or any invert, in that tank. Using copper in a DT is a huge mistake and should never be done. IMO & IME: the chances of curing velvet and saving the fish using copper in a DT are next to zero.You say you're rebuilding after a massive loss; why in the world don't you use a QT?