The Matala Circle Diffuser is self-weighted and flexible. It does not exert any back pressure. Your air pump will run cooler and more efficiently with these air diffusers. 3/8″, 1/2″ and 5/8″ barb. Weighted Circle Air Diffuser: A simple, effective, reliable way to aerate. Made from high-efficiency rubber with specially designed pore size. Numerous pores maximize fine bubble distribution evenly released in the water. Low back pressure | Recommended Air Flow: 0.30 CFM Made from Recycled Rubber, it's durable with low start up, maintenance and replacement cost. Circular style membrane helps distribute the fine bubbles evenly. Includes multi-barb hose connection with 4 different hose sizes | 3/8, 1/2, ⅝. Self weighted, sinks to the bottom automatically. Used in: ponds, lakes, commercial fish farms, Koi ponds, aquaculture, agriculture, wells, rivers, shrimp farms, large aquariums, pool ponds, canals, boat slips, water fountains, waterfalls and more.