Rotating: The bubble stone has a rotating design. The size and density of the bubbles can be adjusted as you spin. Firm: The upper suction cup can firmly fix the air stone in the fish tank, prevent friction and wear, and prolong its service life. Compatible: Suitable for any watt air pump. Application: Oxygenated Aquarium Bubble Stones can add airflow and circulation to your aquarium, pond, hydroponics and aquaculture to oxygenate water and promote aquatic life. Package includes: 2 x air stones, 2 x spare cotton pieces.