This is the Pollen Glass with a wider diffusion filter, which is placed on the side panel of aquarium. Its unique J-shape glass pipe design sits elegantly inside the aquarium tank. 20Ø is designed for 60cm tank with fully grown sun plants, such as Riccia that requires much CO₂ and 30Ø diffuses CO₂ effectively for 75-90cm tank. Pollen Glass Large is made of glass including J-shape parts. Careful handling is required when attaching or detaching suction cup.