No, just letting him be will be enough for him to come back, no fast movements and dim lighting if any lighting at all. I gotta do this with the discus and angels from time to time when they get really stressed over nothing.
The tanks they came from more then likely had a dominant fish in it and their places were established. Cichlids are are aggressive fish and will defend what they consider theirs to the highest hilt with no prejudice. Ive had established angelfish pairs turn on eachother and kill eachother off after years of "peace"
I wish you luck on em.
oops, also putting one in a new tank then adding another could have caused this.
That's not a planted tank. That's a jungle with glass around it- MFDROOKIE Circa 2011