I have used a 40 breeder that was once a QT tank and was hit with copper a few times. I was able to make it a sump for a thriving, invert filled, reef with no ill effects. I didn't use a copper test. I simply took my chances at the time and it turned out working in my, and my livestock's, favor.
I briefly glanced at this-
Copper accumulation... [Comp Biochem Physiol C Toxicol Pharmacol. 2010] - PubMed - NCBI
And before I started to drift off, I noticed that it had different effects on the anemone at different dosages. It's not a case where a tiny bit is going to wipe out everything. How much is the question. Ultimately, none is best.