Cool little fish and great pics guys! If you want to be technical....even a group of 15 chromis hardly constitutes being called a "school". Probably why "most" groups of chromis end up with one dominant fish that slowly wears down the weaker individuals. Could also be that with no large predatory(or perceived predatory) fish in the tank the "need" to school isnt there. It sounds though like the cardinals may be a better choice for a school as they dont have that ingrained aggressive streak that the damsels have.