Hmm. Can't say I'm surprised haha. The strigosus can be real jerks. Nori availability and ample hiding zones will help. Maybe a bit more time in the acclimation box like you suggest. Make sure the tristis is really well fed and bulked up too. That will help it weather the inevitable greeting when he does come out of the the box again. There's no magic secret to adding tangs to a display piecemeal unfortunately. My secret for clients is I put in all the tangs at once, or in 2 sets depending on the tank. Best case is I can QT them all together, but sometimes that's not feasible and some have already been in a post QT holding tank. Even so the principle remains the same- add the tangs before anyone has set territories and there tends to be minimal targeted aggression before a stable hierarchy is established. I put a unicorn, regal blue, purple, orange shoulder, and hybrid powder into one of my personal tanks all on the same day and there were only a few skirmishes for the next couple days but nothing severe. Some of the size differences were pretty significant too.. Good luck with the compatibility! Every fish has it's quirks for better or worse
Thank you so much for the feedback here. I anticipated some issues - it seems worse when it actually happens. I really need to get a sterile tank setup for transfer and "rehab" - I'm just pretty maxed out on space with a fish QT, coral QT, and display in my apartment. I'll follow your recommendation, and keep the little guy in the box until I can fatten him up a bit.
Thank you!