For a qurantine tank, you should have these times:
Heater
1 Powerhead
Small hangon filter
Copper
For me personally, this quarantine setup has worked successfully. You want to keep the water quality as good as possible. In a small tank like that, especially without a skimmer, your parameters will change rather rapidly. When i have a sick fish, i do a 15% water change & test the water every other day (this is the main filtration for the tank). With this procedure, i have had success thus far. You want to be sure that your sick fish are feeling better and give them a chance to fight the disease.