at my shop we do treat the fish only tanks with copper but only when signs of ilness appear, other than that we dont medicate daily.....in our reef systems, which also house fish, if we have a problem with a fish we move it out and quarentine it in one of the tanks with copper or other meds.....i also agree that its not a good idea to add lfs water into your tank....its jsut a disaster waiting to happen!
good luck
jon