Key Features 6 Pack of 40mm x 40mm Air stone Balls High quality durable and non toxic mineral materials making them safe for use around fish Produces small even air bubbles that provide essential oxygen and aeration in Aquariums Can be used in Aquariums and small ponds. Takes a 4mm Airline tubing with a 2.5w Recommended Air Pump Washable and reusable. Regular cleaning with a brush is recommended to clean off any clogged up debris Water rich in oxygen is essential for happy, healthy fish and plants in your aquarium. Air stones require a pump and airline to get the air to them, these are both available separately in our store. Connects to standard size airline. Made of mineral material.