Most LFS use copper in their fish systems to help keep parasites at bay. I'd get a copper test kit though if you're going to use it in a QT tank. If you have any kind of invert, copper treatments will kill them. As far as the time they can be exposed to it, I really have no idea. I do know, from when I worked at Jack's, that there were fish that we had in the store for several months that didn't seem effected by extended use.