Apologies ahead of time for the minijack of the thread, but some of the info is pertinent to mixing tangs also, as I have a mix of 6 species in my display that get along. Also, there is a great thread dedicated to regal angels that I've contributed to starting a couple of years ago on page two... it's now over 50 pages and has been split due to size... Here's a link to the split thread...
regal angel thread ...
The first issue is getting even one regal angel to settle into captivity. While many people say it's the luck of the draw if you get a feeding specimen, IMO in the right hands the vast majority of Red Sea regals under about 5 inches in the right hands could settle into captivity (Above 5 or 6 inches and the fish are much more reluctant to feed... like trying to get your grandmother to use the internet). A small percentage are exceptional specimens that aapt to a captive diet quickly and aggresively, but most require extra attention that many hobbyists don't give. I call it the "dump and hope" approach... when people just dump a fish into their packed display and hope for the best... with this fish it rarely works, and when it does it's usually in a well maintained and quiet reef tank with little competition... take a look in my gallery and one thing I don't have in my systems is "little competiton"

. Food lasts just seconds...
Therefore, I have a method of quarantine that I've used to good effect with many tough species (regal angels, moorish idols, multibarred angel). Many people think the main idea of quarantine if to keep horrible foreign disease that will ravage and kill your fish, wife and family... that is one reason but not the most important in my view. For fish like regals, adjusting to captive conditions is somewhat of an issue, including not handling stress well and not adjusting to prepared foods quickly or easily for the most part. Allowing your new regal to adjust in an established well maintained system with NO competition, dim light, and lots of live rock to graze on goes a long way. Quarantine IS NOT a 10 or 20 gallon bare aquarium with a piece of PVC and a sponge filter. This adds stress, does not allow for grazing, has an unstable nitrogen cycle, and will pretty much do in your regal... Allowing your fish to RELAX for the first few days does wonders... without competition you're able to throw food at them with the object of getting SOMETHING in their stomach as quickly as possible... clams and mussels on the half shell work wonders and will very often tide the fish over until they accept prepaed foods from the water column... remember that for many fish like regals EVERYTHING they eat is off of the reef and not from the water column. One trick I've used is to stuff the clam with prepared foods to fool the regal. Anyway, after a few weeks to months depending on the specimen they are feeding aggresively and ready for the next step... now comes the introduction to its conspecifics!
When I added my trio of regals (similar methods in pairing chrysurus angels, multiple species of tangs) the basic idea is to allow the fish to see eachother without allowing them to touch. On my 6 foot frag tank I have about half dedicated to divisions divided by eggcrate. I've also used "critter keepers" when introducing a new tang to the display. Many times the tang to tang aggression is short-lived and allowing the established fish to see the new fish for a couple of days sharply cuts down on aggression. With the regals, I kept them seperate but able to see each other for a while and then let them meet and greet! Interestngly, the two larger at about 4 and a half inches when I got them hd more issues with eachother than with the smaller 3 incher... Compared with mixing other larger genus angels there was little issues... there are a few people with pairs also that experienced little issues...
Anyway I'll get off of my soapbox, but this is a snipet above... the regal angel thread is a great source of info with a ton of firsthand experience...
The larger two could be seen in my avatar... I'll refrain from posting pics as this is a large enough highjack as it is... pics are in my gallery...
Copps