Pollen Glass beetle is a CO2 / Air diffuser for aquarium, which virtually pollinates the entire aquarium with tiny carbon dioxide / air bubbles. Pollen Glass is hand made from high quality Japanese glass. Unique design Beetle sits conveniently on an inside corner of an aquarium tank. For a large size tank, Beetle can be placed on multiple numbers of corners. SIZE AND DIAMETER: *Pollen Glass Beetle 30Ø is suitable for 90cm size tank *Pollen Glass Beetle 40Ø for 90-120cm tank *Pollen Glass Beetle 50Ø for 120-180cm tank ** PRODUCT IS DIAMETER 30 for 90cm tank