I would only have one. If you have two or three, the dominant one will make the other(s) miserable, which wouldnt be good. Your tank isnt big enought to have enough fish to spread out the aggression, so one is best. You might be able to have some fish like giant danios for dithers, jack dempseys usually hide alot. If youre looking for a personable cichlid, a jack dempsey isnt really a great choice.