JimM

Are you going to be adding to your main tank, ie are you already fully stocked?

If yes, then frag tank plumbed to the main.
If no, then QT. I'd run it without a sump/fuge.

Let me add some more noise to the equation though. Why not a wholly new tank, like a macro/lagoon type setup or maybe a biotope?

I'd vote for QT tank. We all know it is a good idea to have one, although it is tricky to maintain a healthy one...

If you dont already have a qt, then make it a qt.

why not a frag tank that you qt new items in? you can do both with that, also you can qt some smaller fish in there with frags, but i say independently as a frag/qt

I don't think you can have a frag + QT tank. A QT tank is there for disease prevention, you quarantine new fish so that they develop any disease they might have, overcome it, and get moved into DT after a number of weeks in healthy condition. Same thing for corals you QT, you want to see if pests like flatworms appear, etc.

If you use it also as a frag tank you'll have to treat all the other corals and/pr live rock to eliminate disease vectors or pests in case they appear in the fish/coral you quarantine, That wouldn't work.

I understand you need to be able to wipe the QT clean, using stuff that kills pests and diseases, between uses.

would go with a qt tank too very handy!

Thanks all for your insights... I guess a QT it is! Now just one more thing... how do I establish it? I have seen pics here and other places of QT's that appear to be pretty bare bones tanks... not much sand or LR to speak of. What precisely should or should not a QT contain. Do I keep it set up 24/7 or just when I need it. The DT has only just begun relatively speaking... about 8 fish, two small softies and a small rose bubble nem.... with a bunch of inverts.
????
Jim

I think most people run theirs 24/7. Do water changes from the main tank.

If you want to just set it up as needed, you could either keep some live rock in your existing sump that you can remove and drop in QT or run a hob filter on the sump and then transfer when you QT. You would need to let the rock dry in between uses I think, just for optimum safety. Of course, if you medicate the QT that is a whole other ball of wax to contend with.

Either way, bare bones is the way to go; pvc pipe works for hiding spots and can be sanitized easily, a heater, and minimal lights(unless you QT corals too).