Hydrofarm Active Aqua AS8RD Round Air Stone, 8 Inch The micro-pore design energizes your growing solution as it aerates and circulates your nutrients Active aqua extra large 8-1/2-inch air stone disc is a great way to add oxygen to your hydroponic growing system It will extend the life of your nutrient solutions Help keep your roots healthy and promote exceptional growth Air inlet size is 8-mm inside diameter