It`s no secret to seasoned hobbyists that you can expect microbubbles from any skimmer, at any point in time, which can be caused by many factors that can include: additives, greasy food, new filter socks, etc. The Bubble Stopper easily attaches to the outlet of the HOB-1.5 to reduce microbubbles, or to be used as a precaution to microbubbles entering the aquarium.