An airstone is what you connect to your air hose to control the bubbles. You can get airstones for tiny bubbles, big bubbles, or even a buttle wall. You can also connect your hose to decorations like treasure chests which use the bubbles as part of the decoration, and make them move.
I think that underwater bubble river would be really cool. If someone ever gets one you have to share pictures of it with us. 8)