The best air disc available on planet earth is the 8" diameter aluminum oxide airstone. It's a blue colored air disc like all the others , but of all the round air discs this size is the only one made with aluminum oxide. It cannot disintegrate over time and is easily cleaned by drying it out and immersing in a dilute acid (hardware store 31.45% muriatic acid [HCl] watered down 6:1 to get it around 5% HCl). The maximum output of this airstone is 20L/min but it is not necessary or advisable to run at full blast because excess pressure will crack the black ABS bottom casing, so a 3/8" or 1/2" pvc ball valve online with the hose can reduce the airflow to safe levels. The most efficient pump/ stone combination is achieved with a Danner Pondmaster AP-100 (6.53cfm) and 12 discs valved accordingly so that the stones output is at 75% of the max. The replacement diaphragms for the pump are about $10 and the stones can be placed as low as 10 feet below the water surface with this pump, but of course the lower you put your stones below the surface, the more back pressure you will give the diaphragm resulting in less stones being capable of delivering air (the diaphragm will have to be replaced in a much shorter time interval if stressed to the max) to the water columns. The reason why I like this stone the best is because of the 8" diameter footprint. It achieves the most surface agitation of any other stone. It's the agitation at the surface that counts and not neccessarily the amount of air output of the stone that counts. As the air travels up from the stone it pulls water and air down toward the bottom of the water column.