Well... I had a better reply... but I accidentally refreshed the page... so I'm going to be lazy and sum it up haha.
I understand why you preventative treat (and why alot of "pros" do as well) as it really is the safest way to do things, as you said its hard to QT your entire displays worth of fish (even more so with larger systems). I just like to minamize stress, even more so when they are already very stressed from shipping, relocation, acclimation etc, as I've found that when fish get stressed, by being underfed, shipping, poor water, etc they are more likely to get sick, be that infection or parasites, where as when they are healthy, they they rarely get or pass on infections/parasites (as you mentioned). Essentially I QT them untill they are fully "healthy" and fat, medicating if nessisary, then I place them in a large "breeders box" (with more holes for better flow and what not) for a week or more, to help let the display tank fish adjust to the new addition(s), I've found it helps reduce agression occationally.
If I may make a suggestion, possibly do dips instead of full time medicating? To reduce long term stress (even though dips can be stressful depending on the way you capture them). Do you use UV on your QT? I use UV, and a skimmer on my QTs, which is funny, as I don't even use a skimmer on my displays... LOL but I find that UV/heavy skimming replaces the need for heavy medication, as it kills or removes most if not all waterborn parasites/infections. I also use bare bottom QTs so I can clean them more effectively.
I understand why you preventative treat (and why alot of "pros" do as well) as it really is the safest way to do things, as you said its hard to QT your entire displays worth of fish (even more so with larger systems). I just like to minamize stress, even more so when they are already very stressed from shipping, relocation, acclimation etc, as I've found that when fish get stressed, by being underfed, shipping, poor water, etc they are more likely to get sick, be that infection or parasites, where as when they are healthy, they they rarely get or pass on infections/parasites (as you mentioned). Essentially I QT them untill they are fully "healthy" and fat, medicating if nessisary, then I place them in a large "breeders box" (with more holes for better flow and what not) for a week or more, to help let the display tank fish adjust to the new addition(s), I've found it helps reduce agression occationally.
If I may make a suggestion, possibly do dips instead of full time medicating? To reduce long term stress (even though dips can be stressful depending on the way you capture them). Do you use UV on your QT? I use UV, and a skimmer on my QTs, which is funny, as I don't even use a skimmer on my displays... LOL but I find that UV/heavy skimming replaces the need for heavy medication, as it kills or removes most if not all waterborn parasites/infections. I also use bare bottom QTs so I can clean them more effectively.