To clean an air stone, start by washing it in clean water and using a brush to remove any debris. Let it dry for 15 minutes. Then, boil the air stone in water for 15 minutes and let it dry again. Next, create a solution with one part bleach and three parts water. Soak the air stone in the solution for 8 to 12 hours. After that, remove the air stone and connect it to an air pump in a bucket of clean water. Let it run for 10 minutes. Finally, remove the air stone from the pump and let it dry for 12 hours before placing it back in the tank.