I would like to find a schooling fish that is really hardy. I dont really like red eye tetras or danios. My neon and cardinals die all the time and am looking for something that will last longer.
How many gallons is the tank and what do you have in there now?
although they aren't considered "schooling" fish i really like my cherry barbs. Ideally, you could increase your cardinals...but as a second choice the cherry barbs are great and always actively engaged with each other.