I have been doing alot of research for a schooling fish for my 220. There is a big thread on RC about long term success with a school of chromis. There are very, very very few people who have more than two left after a year. The reports are that they tend to slowly kill each other off until there is one or two. This is my experinece as well.
After alot of research I am planning on putting a fairly large school (10-15) of threadfin cardinals in my tank. After hourrs of research they appear to be one of, if not the only fish that will consistently school in an aquarium and one that people have long term success with. They are small, getting to only about two inches. The hard part is finding them.