Personally, I stay away from Central American cichlids in anything less than a 40 breeder, simply because of aggression issues. Even a pair of convicts can be a problem if the male is ready to spawn and the female isn't; he will hound the female constantly. A pair of cons is hit or miss, IME. A pair of convicts and a blue acara is askin' for trouble. The acara will never get any peace when the cons spawn and there is not enough room to run. It will likely end up dead. A 29 gallon just doesn't have enough of a footprint to allow for enough hiding places.
If yer willing to expand away from CA cichlids, a breeding pair of the majority of the 3"-4" Neolamprologus, Julidochromis or Telmatochromis species from Lake Tanganyika, a pair or trio of any of the South American dwarf cichlids (apistos, rams,Taeniacara, Nannacara, Dicrossus, etc.), a pair of any of the smaller West African cichlids, or two or three pairs of any of the shell dwellers fom Lake Tanganyika are all viable options if ya want cichlid behavior in a smaller tank. With this option, you'd also have some room for a school of 5 or 6 small schooling fish like danios as dithers.
WYite