Creating boundaries for clips

1

i created a bubble clip, when u blow the mic it generates bubbles, problem is, because of the continous blowing, the bubbles gets more and more and this makes the movie lag, and as u blow more and more, the movie ultimately hangs… how can i refresh the movie so that the bubbles will refresh as it appears outside of the movie area or create a boundary where it goes back to 0 when it goes over the height of movie, i tried using the ‘creating snow flakes’ tutorial but it doesnt work, thanks a lot, haf a great day