I don't know why these triggers (and Sargassums) are considered planktivores. They are pelagic and usually hang around floating mats of sargassum feeding on small fish and crustaceans. (I could be wrong on this, but have seen some papers on the feeding habits of them.)
Anyway, I kept pairs of both Crosshatches and Bluechins prior to Katrina. I lost my notes in the storm, but remember buying the Crosshatches in the spring of 2003 and I already had the Bluechins. So they were together for at 2 1/2 years. They were in a 240 and there were no problems at all. The fact that both were bonded pairs may have helped, but BCs especially are very wussy triggers. I would expect a little pecking order stuff, but I doubt it would last. It is not impossible that an adult of any of these triggers could see a smaller fish as lunch.Just a thought: sell the BC and get a pair of CHs. They really behave like a true pair and are magnificent fish. Personally, now don't get mad, I just think BCs are boring and reclusive---especially for triggers.