Well, you're not taking into account that they're a schooling fish. Three fish is not a school--it's three fish. I don't know what sources you're using, but it doesn't make logical sense to assume that a fish that swims in schools of hundreds or even thousands of individuals in nature would be happy with just two others of their own kind. With any social fish, even non-schoolers like goldfish, the more the merrier. They will be happier, healthier, and live longer in larger groups.
Looking at your signature, you should really research the social needs of your fish as well as the growth potential of your crayfish. Your kuhli would be much happier with a school of other kuhlis, and many crayfish sold in pet stores get quite large and end up eating small fish like guppies.
Last edited by Adastra; 09-17-2010 at 07:42 PM.