I usually stay out of the disease forum because I get slammed for using copper, but I started out in this hobby long ago when copper was the cure for parasites. I have always relied on copper, and with careful application, it is very effective. I ran a LFS with a permanently set up hospital tank that I always kept copper in. It never had high ammonia or nitrites. It was an established system that ran for years like that. How do you explain you statement that copper kills ALL bacteria (good and bad), if I could run that system for so long with copper?
And to the thread starter, you may want to reconsider copper for your lion and cowfish, they do not do well with copper.