No I don't QT because my LFS do for 6 weeks. And yes they really DO QT and don't just say they do. I will upgrade within a year or two. And probably a 120g.
Glad to hear that your LFS quarantines. The better question is how do they quarantine? Some will just keep them in an observation tank for one or two weeks. That's not an effective quarantine. Some will run copper in their tanks, but most don't use enough of it for it to truly be effective. For these reasons, unless you are really tight with your LFS and know exactly what they do and that they do it every time, without fail, most reefers will do their own quarantine.
Why wait on the upgrade? Do it now. The tank and stand are usually the cheapest part of the upgrade. Keep all your old equipment and just get the benefit of the additional space and water volume. I see you're new here from your post count. Most of us have seen this question a thousand times over, with the promise of "I"ll upgrade soon." I don't think the upgrade happens as often or as soon as most promise. You're getting the response of many experience reefers who are tired of seeing the same mistakes over and over again. Don't take it personally. We've all been there, doing things that are not in our fishes best interest. We just think it would be a good idea if you benefited from some of the collective wisdom.
I've had a 10 inch vlamingi tang, 9 inch hippo tang, 5 inch yellow tang, 4 inch kole tang, 3.5 Inch Tomini tang, 6 inch sailfin tang, and a 4 inch powder blue all in my tank at the same time without any compatibility issues. But then, my tank is a 6 ft 250 g.
It's not that you can't put tangs in a 4 ft long tank, it is just putting the odds against you and your fish. Less swimming room for overall health and smaller spaces mean a greater chance of bad interactions. Think how you would like living in a small house with 8 other people, falling all over each other.
I had a 4 ft 150g tank before my current one and I didn't realize how much better that extra 2 foot was until I got the new tank. Even now there are times when I wish I had an 8 foot tank, but that isn't going to happen.
As Harry Callahan said, "[a] man's got to know his limitations."
