I would actually question the choices of your LFS
if these are the fish being recommended for a 55 gal
tank. When reading your profile it also states the tank is only six weeks old?
For the speed of additions and aggressive types of fish, I'm actually a little suprised you have not lost more fish. To be honest, you have far too many large growing active fish for that size tank (sorry). It is not suprising that the wrasse killed the royal gramma. It will not be long before it also attacks the hogfish (also a wrasse) and especially the bar/dragon goby. Large wrasses (especially from the thalassoma
species) usually kill smaller fish on sight when newly introduced. Wrasses can be tolerant of each other in larger systems but will most often fight in smaller tanks and especially when in cramped spaces due to other fish.
You need to scale back the amount and types of fish in your tank to keep the animals successfully. The tang, lunare and hogfish should not be in that size tank. They would all be much better off in a 90 gal
or larger and only one at that. If you wish to keep all three f these fish I would recommend no less than a 150 gal
If you remove the larger species, keep the angel, goby and clown; you would still have space for one or two smaller growing species to complete the tank. Keep in mind that when aquiring animals, you need to choose them with their maximum adult size in mind not the size at the time of purchase. The recommended guideline is 1" of fish for every 5 gal
of tank not including the tail. So for a 55 gal
tank that's 11" of fish give or take. This is only a guideline and not a factual rule but in this case it strongly applies. 6" lunare, 6" spotted hog, 6" yellow tang, 2" flameback, 3" bar goby, 2-3" tomato clown. As you can see it adds up quickly...