AERATOR FOR YOUR TANK: provides your fish with a better supply of oxygen. CAN BE BURIED: for a cleaner look, bury this air stone under your gravel or substrate. SIZE OPTIONS: this Air Stone is 4 inches long, but it is available sized 6 and 12 inches, as well. (Each sold separately.) TUBING NOT INCLUDED: airline tubing can be purchased separately SHOP PENN PLAX: for all your other aquarium needs, everything from nets and thermometers to air tubing and filters.