I don't agree with "fishprotector". In my experience, barbs are not good fish for kribensis cichlids. Kribs are very placid and gentle fish, which don't normally dart about. In the case of barbs, they are quick moving and mindless; more so when they are in a small tank (20g isn't super big). If you wan't the kribensis, then go for them. Do not leave them with the barbs though. They stress the kribs out and I've seen kribs loose a lot of their confidence in the tank because of this. Sometimes the kribs get murderous and decide to take down the barbs. If you wanted to keep the BN with the kribs, and give them several caves- then I say go for it. I could also see the platies being eaten if they are small enough.