What's your attraction to a predator fish. My attraction is their stalking and hunting nature which I preserve in the tanks I keep. If you have one in mind for their beauty then feeding them live prey or training them to eat dead food wouldn't matter either way. A lionfish would be a good choice for a tank like that, is the reason you are not interested in keeping one because they are poisonous. If so that would also rule out scorpionfish and the like, and these guys aren't as entertaining as a lionfish. Anglers are another choice in predator fish, again rather stationary and alot of tank for a immobile ambush predator. The tanks too small for any bad a triggerfish and they would make a mess of the macro/xenia. Although not commonly considered predators; hawkfish and some wrasses could be considered predators, they would gladly hunt down ghosties and small fish. How about a smaller fang tooth eel, like a jeweled or yellowhead. I consider a predator tank, a tank being fed live prey.