Using a QT tank is ALWAYS best. - I will NEVER add a fish directly into my tank with out QT. - Me personally. - Some will agree some will disagree.
Here is how I do it.
I have a QT tank. - Its constantly running. (ALWAYS)
Inside the tank I have simply sand. - The room I keep it in is low lit so the fish have minimal stress to things moving around it..etc.
Now - When I am about ready to purchase a fish that I have researched and like, I will drain the tank, and fill it with water from my display. - Meaning same levels that are in my tank the fish will be exposed to.
Day 1.
-Drip fish for 20 minutes.
-Leave fish alone for 1 day.
Day 2.
Feed fish (Use foods with vitamins and garlic)
Day 3 - 10 continue
Day 11-14
Change out 25% of water with current display tank water
Day 15
By now you should have noticed any parasites, eatting problems etc. - If your fish appears to be healthy he is already adjusted to your water of your tank,temp etc.
Night - Day 15 -
Add fish once your display lights have turned off - He is going to be in a new surrounding and you do NOT want other fish picking on him ...etc
Day 16
I keep my MH's off, and 2 of my 4 PC's off.
Tank is low lit... perfect for adapting
Day 17
Fish is ready, healthy safe, fat and eating perfectly.
NEVER had a problem.
Over protective? - YES - But these fish are expensive, We have removed them from there natural habitat and its only far we give them a fighting chance.
Take care of our underwater allies.