Aquarium Bubble Stones / Air Diffusers / Air Stones / Aerators - twin pack, manufactured by BubbleMac Industries, Inc. - makers of "The Forever Bubble Stone", High-Quality, 100% Glass-Bonded Silica Air Diffusers High-Quality American Made Air Diffuser. UNLIKE the blue import bubble stones, this diffuser is low maintenance, durable and lasts a long time. {THIS IS NOT A DISCARD-A-STONE.} -- DON'T WASTE ANOTHER DOLLAR ON THE BLUE STONES WHICH SEEM TO "DISSAPPEAR" OVER A SHORT TIME?? Manufactured from 100% Glass-Bonded Silica, this airstone has been the renouned worldwide for the past 30+ years as "the most efficient way to increase dissolved oxygen levels in a tank." Now available in an aquarium application. Standard Air Line Connection, 5/32". Self-Weighted and Non-Clogging. Bubble-stones increase surface agitation and oxygen levels, eliminating "dead" spots / stratification. Bubblemac Air Diffusers Promote Healthier Fish by Reducing Stress. "Ya'll Got Bubbles"? - SPECS: 100 Glass-Bonded Silica. Maximum Pore Size 140 Microns, Nominal Partical Retention 50 Microns, Flexural Strength 2500 PSI, Bubble Size 1-3 MM, UNLIMITED LIFETIME When Used in pH of 8.0 or Less!