The use of copper by many LFS
is quite common. If fact most all FO
tanks at the LFS
will contain some type of med to at least restrict the spread of parasite problems. Just as frequently though, the levels of these "pervenative" additions are not closely monitored and usually at best keep things at bay and are not concentrated enough to be an effective cure. That said though, I would rather buy from an LFS
that uses some sort or prevention rather than none. If your careful and fish are always introduced to the QT
before the main tank, there is no reason for any concern.
As far as maintaining "theraputic" levels of copper, I would advise against it. Long term exsposure to copper will damage internal organs and continually supress the fish's natural immune response leaving in open to a wide variety of fungal and bacterial problems. The main thing to distinguish here between the LFS
and home use is the fish are not typically left in the holding tank at the LFS
for very long and if needing to treat at home, the length is usually only 3-4 weeks at most for copper. As with any treatment copper or otherwise, all have drawbacks but if for only short periods will not normally casue permanent damage.