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I have a 180 Display... I love tangs... Anthias... Wrasses... My current favorites are my Blue Jaw Trigger and Convict Tang. What would be cool in a tank like yours is a harem of tangs.... I have seen guys do that with small yellows... 6 plus.. putting them all in at the same time. The key would be if you can get small ones from somewhere like LiveAquaria. In a big reef tank ... the color and the activity is pretty cool. Another cool tang to do that with would be with some Carribean blue tangs. The juvi's are all yellow like a yellow tang but will morph over time.
The other thing I would do is have all sorts of anthias. Bicolor, Lyretails... are really cool in large groups.