[FishyFishy!]

I would personally never medicate a display tank. I would always get a QT and run a HOB filter with floss and bio media only.

What I do is have a HOB filter running on my Display or display sump at all times to keep it cycled. Then when I have a problem, I fill my 30 Gallon QT with tank water in the form of a water change on the display. Then transfer my already cycled HOB filter to my QT tank. Then medicate until they are better.

Once better, I do a water change on the QT, wait another week or two, then put them back in the Display tank after a drip. I then usually dump the media from the HOB filter in the garbage and do a good cleaning/bleach/water bath on the filter unit before placing it back on my Display sump with brand new filter media.

Since starting to do this method I haven't lost a single fish to illness, and actually haven't had an outbreak of anything in a long time (knock on wood).

In answers to your other questions, I think a 10-30 gallon tank is ok. I use a 30 and it works fine. Conditioned tap water should be fine. I use PRIME, it's the best IMO. Leave fish in for at least 2 weeks of treatment. Then another week or more for Quarantein to watch them afterwords. Medicating is not a fun process!