Sorry, did you say 215 gallons? I had mine in a 1090 gallon system and the skimmer was nasty every day! I mean NASTY! I had two Vlamingi, a Black Unicorn and two large Nasos. So uh, 215 is way too small for any of the fish you montioned. NO, they do not grow to just be the size of the tank. They grow to be their natural 19" -22" size. So your problem has to do with water quality.
I had two skimmers running a G4 and G5 and that wasn't enough. You need to be realistic man, who is going to take those tangs when they get to big for your 215? I was lucky and Fish Gallery agreed to take mine and NEVER sell them. But they will undoubtly not want yours with holes in their head and mine being all fat and tasty.
Sorry for being so blunt. But that is how I am am, please come back to reality where we are responsible reef keepers and keep fish that are not doomed to a post on this board at some time in their future "Anyone want a really huge Vlamingi?"
I hate to be so rude, but have you done your reasearch? How many inches of fish per gallon is it? And yeah they are small now but base that off of full grown size, and assume you aren't going to kill it before it gets too big. Man I am mad at seeing this post!
I was very attached to my Nasos and Vlamingi's and thought if I built a 700 system they would be ok, but even then they overwhelmed the system to the point I had to get rid of them. They should be like the Nautilus, DON'T DO IT, should be by their name in the books.
If you really need to know what to feed them go to the Vietnamesse grocery store and get Norii and Red Algae and get Omega One Fiah food, sold at GUESS WHERE? Fish Gallery and Pet Boutique too I think.
Stop with the frozen as anything but treats and brine has no nutritinal value it is like feeding your Iguana lettuce.
Anymore brow beating you need? Let me know so I can beat you up MORE for getting those tangs in a 215! I have been there and done that, please stop killing them! Get a bigger skimmer and keep your water cleaner. Frozen when not strained has alot of junk you don't want in your tank too.