well all depends on the aggressive mentality of a given fish. 240 gallon can work or even 300 gallon will fail.midas, flowerhorn trimac or red devil are all aggressive fishes. a strong male will try to dominate the entire tank. if 2 or 3 strong male are present there will be recurring fighting one dominating at a given time while others are waiting for moment to take over.with strong male flowerhorn and midas hope for peace is luck dependent. they may live together or may fight.you will have to observe their action towards one another for 4-6 months before taking any permanent decision.