Weighted to sink Modular height Easy to clean Keep your aquarium well-oxygenated by using an air stone with your air pump. An air stone is used to diffuse the air into smaller bubbles that agitate the water surface and increase oxygen levels. We built our weighted air stones with little, modular discs that can be snapped together or removed to create the perfect size. Plus, its small diameter is perfect for fitting inside common air-driven devices, like sponge filters.