Like has been mentioned I would only go with a pair in a 6g. If you had 3, then the tank should have tons of plants and other objects to help the little guys hide and stay away from each other. I have 4 in a 20g long and all I've been able to get them to eat is bloodworms, brine shrimp, and of course snails.
They do have tons of personality. Every time I pass by the tank, they come to the front of it. I can sit in front of the tanks for a while just watching the little guys hunt down some food. They also seem to eye ball me alot.