"Removing" members from a bloon
When you "remove" a member of a bloon, they will no longer receive messages and notifications related to the bloon, and the bloon will disappear from their sidebar. If the bloon is open, however — as newly created bloons are by default — they will still be able to see the bloon in the list of open bloons and rejoin it whenever they desire.
If the bloon is set to secret, the removed member will not be able to rejoin the bloon unless re-invited.
If the removed member is not a member of the space but just a guest, they will be unable to rejoin the bloon without invitation regardless of whether the bloon is open or secret.