I don't treat. I observe until and unless something manifests, like ich, etc. [I haven't seen a case of ich since about 2005, and part of that is caution in buying fish, and buying from a shop that itself takes precautions.] Then if I have to treat, I can choose the right med for what the fish actually has, instead of treating with something, then having to clear out one med in order to treat with another (by which time the fish is already suffering from the first med.) Copper is a pretty rough med that can damage a fish, especially if it comes from a place that has already used it; and some species of fish (angels, eg) are particularly sensitive to the treatment. I think we have a list of fishes that react to it in the Fish Disease forum, in the thread about meds and treatments. TTM is a really good treatment, but as aforesaid, ich is so rare for me, in the stores I use, I just wait until I see something.