4 Inch Round Air Stones for Aquarium Fish Tank Hydroponic Systems Active aqua 4-inch air stone disc is a great way to add oxygen to your hydroponic growing system The micro-pore design energizes your growing solution as it aerates and circulates your nutrients Help keep your roots healthy and promote exceptional growth Connector Diameter: 4mm Approx Size: 107 x 19m/4 x 3/4(Dia.*H)