as someone else said, that is not a school. that is a ball of stressed fish, my guess is that it is probably brought on when they are stressed and attempt to retreat to their host. with no natural host available they just form into a tight ball. it is not a natural behavior and you certainly shouldn't use it to justify your attempt to keep a large group of clowns together.
take the advice from your first thread, come back in a few months and tell us what has happened. and when you end up killing a few fish I hope you feel good about yourself