Hmm, I use copper safe. Again it is chelated, but at the 1 tea per gal. Has been effective. I have added a 1/4 of a tea extra when improvement wasn't seen in 2 days. After that it never showed again
Hmm, I'am one of the few that still uses copper bc it wrks so fast. It has to be at too low of a level. Also unless needed maybe ease off the water changes.
Urchins will be fine. They do eat alage. Mine will eat seaweed that I feed the tangs. The coral banded do have a rep of getting aggressive as they age tho