Kordon "Mist-Air" Coarse Airstone is the rugged general purpose airstone with a number of advantages. Kordon "Mist-Air" (Bonded Glass Bead) coarse Airstone's can be connected by standard 1/4" OD flexible tubing to any regular aquarium pump. Its large bubble size is the best at removing gases (such as carbon dioxide) from the water. It is the best airstone for undergravel filters because of it ability to lift the most water.