I use NSW in both of my tanks, and haven't quarantined, I know that's a hot issue but the only times I have run into problems is when something equipment wise went wrong. For instance, the hurricane before last the power went out, and I was not properly prepared, long story short, the fish got stressed and I lost 2 clowns and a file fish to ich, a firefish flashed a lot but survived and is still with me today. But I was devastated. Once power restored I kept everything going but waited a month or two before I added 2 more clowns and a coris wrasse, current info on ich would suggest these new fish would or should have gotten ich, going over a year now, no signs, still using NSW from the inlet. My 90gal has a yellow tang, gramma, 2 clowns, they started showing signs of ich earlier this year, I found that my tank heater glass was broken and didn't realize it till I was getting little shocks if I touched the lights with my hand in the water, I immediately went and bought a new heater, started feeding a little more than usual (LRS) just to try and build their health and immunity back up, even went and harvested some oysters from the inlet and fed them that. Those fish are still with me today and happy as ever, ich cleared up and Ive added a tailspot, file fish (from the ocean), and the coris wrasse from my small tank with no problems so far. PaulB has a lot of insight on fish immunity and I took a chance with it and glad I did, this is all my humble opinion though. I was in your position, should I set up a quarantine? Do I need one? In the end, never did, and probably wont. Not saying its not a bad idea but I think it stresses them out more helps.