Scrabble?! AIRSTOP

Definitions of AIRSTOP in various dictionaries:

An airstone, also called an aquarium bubbler, is a piece of aquarium furniture, traditionally a piece of limewood or porous stone, whose purpose is to gradually diffuse air into the tank, eliminating the noise and large bubbles of conventional air filtration systems, and providing other benefits to the health of the fish. "Airstone" is also a brand name stone or brick veneer used by homebuilders. Airstones are sold in a very wide variety of shapes, sizes, and levels of coarseness – from extremely rough, producing larger (though still typically unnoticeable) bubbles and letting in more oxygen – to very fine, producing minuscule bubbles. Airstones are increasingly being made from bonded glass beads and synthetic products like fiberglass. There is some controversy as to the efficiency of airstones versus the conventional powerhead system. Arguments can be made in favor of both systems, and both possess certain advantages and disadvantages. Among aquarists, the choice is very much a matter of personal preference, quite often discussed in internet forums.