YES! Qt., don't just treat will nilly! What if the fish is perfectly healthy, and here you are treating it for worms it doesn't have, or even using Maracyn, which is an antibiotic (we all know the dangers of using antibiotics indiscriminately--it can encourage super bugs and then not even people will have antibiotics that work!) We are running out of antibiotics. I hear that in less than a decade, there may not be any more antibiotics that work, DUE TO OVERUSE and that means a lot of animal and human lives will be lost. This is a serious, and terrifying problem. A healthy fish that is stressed from shipping to the store, and then coming home with you doesn't need medications shoved down his throat. In some cases, it can mean the difference between recovering from the stress, or succumbing to it because you stressed him FURTHER.
When I was a vet tech ( and I did it for 12 years, so I learned a lot ) we never treated for parasites unless we knew for sure that a dog or cat had them, because these anti-parasite drugs kill worms, which means they are poison. So you would essentially be poisoning the animal as well as the worms. Why poison the animal unless you have to? Probably not to the extent of killing the animal, but as I said, if the animal is already stressed...
It's just easier all the way around to qt. every new fish you acquire. After battling Columnaris, Camallus (sp, too lazy to look it up) and of course, ich, I've learned the hard way to keep an empty tank handy, and just use water from the main tank, put in a heater and seeded filter, and qt!
Nothing like a dip possible there and as you're treating (if you do) in a tank separate to DT, you are just about into a QT by default. Maybe when those hand scanners (tricorders?) off Star Trek are released next year..
