?Specification? Please be careful to choose the correct size when you buy. Black 13: 13cm, air stone fit for inner diameter 4mm tube; black 21: 20cm, fit for 8mm trachea; white 13: 13cm, suitable for 4mm and 8mm trachea; white 20.7: 20cm, suitable for 4mm and 8mm trachea. Durable: The bubble plate is made at high temperature, and the fine bubbles can increase oxygen levels, reduce CO2, and increase pH. It can also be easily washed for reuse. High Quality Material: The disc uses finely compressed material, and the bubble is small, and the bubble is concentrated on one surface. Adjustable atmosphere plate: the size of the bubble can be adjusted, the smaller the gas volume, the smaller the bubble. Please soak in the aquarium for two hours before use, the effect will be better. If the water depth exceeds 40cm, the power of the air pump can be increased properly. ?Application? Aquarium air stone ideal for freshwater, saltwater, hydroponics, aquatic aquariums, aquariums and ponds. 1 air
