List of open bloons
Viewing the list of open bloons
Click on the "open bloon" symbol () located toward the lower end of the sidebar, as highlighted here.
This brings up a listing of all the open bloons within the current space.
Bear in mind that secret bloons are not included in the list of open bloons.
Joining bloons
You can directly join open bloons from the list of open bloons. Here, the space "DEV TEAM" contains five open bloons. The user is currently a member of four of them — all but "gossip, etc". She can join "gossip, etc" whenever she wishes, by clicking on the plus sign (+) that corresponds to that bloon.
Once we join a bloon, it is immediately added to the menu of bloons in the sidebar.