Lee's Discard-A-Stone plastic air diffusers keep aquarium water circulating with columns of oxygenated air. Coarse bubbles keep water from stagnating. They are an excellent aeration device for use in under gravel filters, corner filters or just as decorations. Includes adapters for airline tubing.
Have been using this for years, but now item is not carried generally in pet stores. Probably newer items have replaced it. It is a pleasure to discover it available through PetGuys, with very fast deiivary.