I was told to put up mirrors against the outside of the tank to distract the aggressor for a while and it worked great for me. I got a yellow and a purple tang that really had it in for each other to become best friends in about two weeks. Might be worth a try. 
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72 gal bowfront reef. multiple zoos, ricordea, and tangs. 2X150 watt metal halide, 2X55 watt cp, and moonlights. 28 gal seahorse tank, with 1 pair of seahorses.
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