It depends on the size of the tank. I've got a pair in a 44 corner and they do fine, always raising a few young that make it to 1/2 inch size (when I take them out). When I spawned them I had a pair raise multiple generations in a 20 long. I'd say in a 55 you could keep 2 pair if you have spawning sites on opposite ends of the tank so they don't fight over one site. They'll spawn in rock caves or broken flower pots. If you get two you're better off with a pair or 2 females if you absolutely don't want fry. The females have a purple tint to their belly. The males usually have a couple of dots on their dorsal.
The local Chedders resturant here has a 400 gallon tank above the bar filled with tinfoil barbs, silver dollars, tiger barbs and bloody parrots. There are 2 pairs of kribs in the tank and one of them has some 1/4 inch fry that they keep in some thick fake plants. It' amazing that they can successfully raise fry in a tank with 100+ predators waiting.