The Oase biOrb Air Stone fits in the base of the biOrb underneath the filter cartridge. It
breaks up the flow of air into the aquarium, splitting it into a mass of
fine bubble. It also reduces noise from the air pump. Over time the tiny pores in the air stone can become blocked by dirt
and lime scale preventing air from getting through properly. Depending
on your local water supply and the conditions in your biOrb an air stone
can last anywhere from 3 months to 3 years. Changing the air stone from time to time is advisable.