There are a lot of urban aquarium myths out there.
New fish should go through a quarantine to insure they are not bringing in anything bad. I normally use 30 days from farmed or tank raised fish and 3 months for wild caught imports. It can take that long for some things to manifest with the problem tha can ride in on fish arriving almost directly from the wild.
Since you have no fish you can actually use and anti-fluke med treatement as a preventative. Whateve rthe direction say on the med is what you should do. When you hit the end of the treatment, you should do two things. First, do as big a water change as you can. Next, rund a bag of carbon in the filter or hanging in the tank where there is flow, If possible in the filter is the best place for this. Run the carbon for a couple of days. ythis way you know 100% there is no residual med in the tank.
As Byron noted, when fish are present this means there are other important considerations. One is that a med which is not needed may do harm to fish or inverts and in some case to one's filter/bacteria. Think of it like chemo for treating cancer. Killing the cancer os worth the risk of any side effects from the treatment. But nobody get chemo unless it is 100% certain they have cancer. It is the same for fish. Unless they are on death's doorstep and you don't know why, only medicate when you know for sure what you are treating.
I have bought fish from breeders, from stores, online and as wild caught imports fresh off the plane. I never treat proactively unless I know what I am treating. Not everyone does this. But there is a difference for a hobbyists with one tank and wholesalers and importers who bring in fish that are worth many 1,000s. One way to minimize the need to treat prpoactively is to make an effort to buy healthy fish. One of these is worth at least 3 DOAS or 5 really sick fish.......
