Lenna,
Sexing orange chromides is difficult. Like most cichlids that share broodcare equally, each sex looks much like the other (most notoriously, as with angelfish). It also depends on the strain; the wild, greenish type is easier to sex that the artificial bright orange type. Typically, males are more brightly coloured than the females at breeding time, but this varies and isn't consistently useful.
I'm told -- but I've not seen this myself -- that orange chromides are among the very few cichlids that can change sex. This is quite common in the damselfish family, which are the closest relatives to the cichlids; anemone fish, for example, routinely change sex depending on which fish is dominant in the social group.
Realistically, as with angels and other non-dimorphic cichlids, the safest approach is to keep a small group and let them pair off naturally. Remove "spare" fish once you have a pair, either to another tank or back to the retailer. In a reasonably large tank (say 100 litres or more) you can probably keep four of five fish without any problems even if one pair does decide to breed.
Personally, I'd recommend keeping the other fish around in case one of the fish in the pair turns out to be a bad parent or infertile. This is not uncommon with inbred, artificial strains. Having "enemies" in the tank with them is also a good way to cement the pair bond, and cichlids that have something to focus their attention on are usually the best parents. Obviously, this is only fair if the spare fish have space and places to hide, so they aren't constantly attacked.
On the whole these are good fish, and funnily enough someone sent me a bit of video of their orange chromides taking their family of fry around the tank. Very, very cute. His fry weren't fed on anything specific, just general aquarium detritus and fine flake. So probably as with kribensis, you'll probably want to let some algae and mulm build up in the tank instead of trying to keep it spotlessly clean.
Cheers,
Neale
