If I may ask, what is your QT process for tangs?
Would the tangs from the same genus work together? For example having a few tangs from the acanthurus genus including clown, orange shoulder etc?
What is your experience with having a pair or trio of yellow or blue tangs?
It's a crapshoot. What you don't see is the evil Achilles that didn't tolerate other Acanthurus so I now have two (moved other to an aggressive tank) and a smaller powder brown that I sold due to bullying and a hybrid PBT that got bullied to death (by the Achilles).
It can be done but you need a plan b and to be vigilant. IMO Acanthurus tangs aren't much harder to mix than zebrasoma but when things DO go wrong it's much more serious. There's a lot more variation in temperament. Orange shoulder are pretty mild. I had a clown tang with that group for 1 month without issue but sold him and opted for the Sohal.
Mixing zebrasoma is a bit easier and they tend to "forgive and forget". Acanthurus tangs do NOT. Particularly powder blue tangs and Achilles tangs that decide they don't like a fish or other fish. That's it. It won't subside. The exception is powder blues with each other, occasionally. If it's an all on war - it won't go away. But if it's sparring often but minimal or no damage it can take a month or so before they tolerate each other well.
For Acanthurus, add them at the same time, and they're the same size. Make your tank is 1000% parasite free because unlike zebrasoma, hippo, some naso tangs, and a few others, the Acanthurus genus can not build a resistance to it. They will eventually succumb if it has ever been in your system.
It may take a week, or a couple months. They'll be ich free for up to a couple weeks but no matter how great your water quality, how often or what you feed, etc. it won't matter. They'll slowly become emaciated because the ich will slowly take over and increasingly rob them of nutrients. They'll have obese bellies from nori and heavy feedings but their spine will show and they'll slowly waste away until they stop eating and die.
There are rare occasions, I kept an Achilles in a tank with ich (and a PBT) for about one year. They both came from another hobbyist who had them for three years prior. They still succumbed eventually. I'm embarrassed to admit that I was that bullheaded and I've killed many trying this.
Other tangs and species really can manage ich. Velvet though is far worse, and other parasites.
My qt procedure is 35 days copper at .5-.6 ppm (cupramine though). And I ran the tanks fallow where Acanthurus tangs will reside to starve the parasite for 72 days (still is progress).
I will also utilize Humblefish's method he does not yet endorse but it will work - 10 days copper as described above and then a tank transfer for 3 days treated with prazi. You can also start prazi for the last 3 days in qt as well. Since it's safe for use in dt reef tanks I'm OK risking it for only 6 days instead of the recommended 10 or so.
Stay away from amquel, prime, and other ammonia nitrate and nitrite detoxifiers while using copper, get a sea chem ammonia badge to detect ammonia during treatment because cupramine will mess up ammonia tests except this one, and do water changes as necessary to minimize ammonia.
