With that level, it takes luck and s****. Some suggest going to the side, I say go right up the middle. You have to get through the bottom level using the least number of bubbles possible. As quickly as possible, try to drop the bubble generator since it screws things up by randomizing color. Look for strings to drop and get to the last color release bubble. It allows you to drop a whole string of like-colored bubbles. It took me several times to break the level. It helped to earn a rainbow boost by replaying easy levels.