Great post ! QT is a vital part of reefing not just for fish but for coral also. It is much easier to treat a fresh coral that is infected in a small qt as well as fish. It is also important to have a qt so if you do find an issue or pest it can be treated quickly. I usually do a water change in my DT to fill my qt. I use a 20 gal is all. You do not need to have a huge qt unless you buy huge fish and coral lol I usually QT fish for a few weeks and coral for 4 to 6 weeks unless I get it from sources that I truly trust and am familiar with their QT practices