How do air stones work? Aquarium air stones & diffusers are placed at the end of airline tubing. An air pump pushes air through the air stone, which is typically made of ceramic or wood. Air is forced through the small pores in the air stone, making fine bubbles. With an air pump and air stone like the Hagen Aqua Fizzzz, aquarium water is circulated and oxygenated, while also helping carbon dioxide to leave the aquarium. Because air stones get clogged, they should be replaced periodically. Although air stones are technically air diffusers, hobbyists often use the term air diffuser to describe larger items, such as a perforated wand that delivers air into the aquarium over a larger distance.