Check the listing for details. Pond Air Diffuser Stainless Steel Weighted Hydroponic Aerator KoiPond Dual Ring. Condition: New. Listed at 89.95 USD. Stainless steel weighted dual air ring for dynamic water movement. Easy to maintain FDA Polyurethane tubing that delivers even micro bubbles and lasts. Replacement bubble tube, if ever needed, is super affordable over having to purchase a whole new stone or rubber membrane model air diffuser. The two rings in their different sizes together create a dynamic movement of water. The rings stay put on the pond bottom where placed. They require less pressure which helps your air pump life due to less demand and less back pressure. 10 1/4" outer ring 6 1/2" inner ring. Pond Aquarium Air Bubble Stone Fish Tank Hydroponics Aerator Dual Ring. Condition is New. Shipped with USPS Priority Package. Optimal air 40 liters to 60 lpm. But works great on a 25lpm air pump! Excellent paired with Hakko air pumps.