What Happened to My Stone?

i noticed today that the ozone is not bubbling out from all over the surface of my stone, instead it is just coming from the very top edge, near where the tube enters the stone. i refitted the tube very very tightly, but it still only comes out that one place. there is a lip where the stone is cut to allow for the tube to enter it. it is right along that lip that the ozone is coming out, nowhere else. this just happened today. weird, anyone know what this is about?