Personally I never get an eel from a source that runs copper. My research has suggested that even sub-therapeutic levels of copper can have negative effects. There are 2 lfs in town that run copper, I've been here for 30 years, I do not know any eels that survive more than several months to about a 1.5 years from these sources. You can call this anecdotal if you choose, but it's 100%, many of the eels die much sooner. When I have influenced hobbyist to get their eels from other sources, they have had eels live for many years; along with a healthy diet and proper husbandry of course. Many hobbyist that have success with many other species, yet for some reason, every eel they get from these sources, die soon afterwards. That's just one point of reference. Here's the facts, eels have a metabolism which process toxins at a slower rate than other fish, this allows these toxins to linger through their liver longer, and the liver is what is responsible for eliminating these toxins. I wish you and the eel well.