Marina Rectangular Airstones Marina Rectangular Airstones – Airstones for aquarium use. The Marina air stones are ideal for adding accents in any aquarium. The air stone diffuses air, also creating water movement. The air stone also increases surface agitation and accelerates oxygen replenishment. It also helps release carbon dioxide build-up. Simply connect the air stone to your airline tubing and place it in the desired location. Rectangular shape. Sizes also available: 10 cm (4”), Rectangular 15 cm (6”), Rectangular 30.5 cm (12”), Rectangular Please use the drop down menu above to select size. Also click here for a wide range of Marina products & accessories!