Just to chime in. I definitely wouldn't put any kind of a trigger fish in a 55 gallon and the idea that somehow a Flame Angel would be okay but a Coral Beauty wouldn't be is just plain silly. The Coral Beauty is actually a better choice in this particular case since they are one of the cheapest and hardiest of the dwarf angels. I would attempt to source one from Fiji if possible (collection methods are better). Just my opinion but they also tend to be less aggressive than the Flame Angel. I agree with some of the other comments here about the Clownfish being a problem. One of the biggest lies told in the hobby is that Ocellaris Clownfish are Peaceful when there are many examples that show them as being semi-aggressive/territorial to some degree, especially once they get established. I had a snowflake occ that wasn't 2 inches long that went after everything in my tank when I first added it and I know for a fact it attacked my scissortail dartfish repeatedly and contributed to it's death as well as the purple firefish. The Royal Gramma should be able to hold it's own against an aggressive fish and it's low cost makes it a solid option. Another option is a Melanurus Wrasse. They are generally peaceful fish but WILL NOT put up with being pushed around. My Clownfish attempted to push around my young Melanurus and found out exactly how bad of an idea that was. The Melanurus took it for a while and then decided the little brat needed to be taught a lesson and spent the next 36 hours attacking the clownfish mercilessly (I even saw it bite the clown by the tail and shake it like a ragdoll). After 36 hours it backed off, only giving the clown a little reminder nip every now and then to keep it in check. The clownfish never dared to chase or bite it after that. My Melanurus also put up with some new guy "pecking order" garbage from my Yellow Tang and Coral Beauty, it didn't care that both fish were technically larger than it and took both of them on (even going after the Yellow Tang's tail scalpel and all). Despite the aggression from my butthead of a Yellow Tang he NEVER attempted to bite or hit my Melanurus with it's tail scalpel as he knew there was a good chance it wouldn't end well. Add in the Melanurus Wrasses color, personality, level of activity, generally hardy nature and low cost and it makes them a pretty decent choice for that tank. Be aware though that they do require a sand bed to sleep in and they can periodically pick off snails, hermit crabs and ornamental shrimp.