Noun
airstone (plural airstones)
English Wikipedia has an article on:airstoneWikipedia
A piece of aquarium furniture, traditionally limewood or porous stone, whose purpose is to diffuse oxygen gradually into the tank, eliminating the noise and large bubbles of conventional air filtration systems.
As with deep water culture, there is an airstone in the reservoir that pumps air into the water via a hose from outside the reservoir. Source: Internet
Both the airstone and the water pump run 24 hours a day. Source: Internet