What kind of "predator" tank do you want? There are a lot of choices and different kinds of predators.
You can keep corals with some of the slow moving ambush predators, like scorpionfish, lions, marine bettas, groupers, etc. You just have to watch that the high bioload. If you want to stay with a literal predator definition, you could even consider seahorses for a predator tank, as long as you kept them with compatible tankmates.
What kind of fish do you like? My favorites for personality, which happen to be fish that would bother corals, are puffers and triggers.
You might be able to keep a dogface puffer or larger sharpnose puffer, a smaller trigger (like a picasso or niger) and a moderate sized eel, like a snowflake, in that tank.