A 30mm round airstone is a compact, porous diffuser—typically made of ceramic, mineral, or sintered materials—designed to attach to a standard air pump via 4mm silicone airline tubing. Its primary function is to break airflow into fine, oxygen-rich micro-bubbles, which improves water oxygenation, enhances circulation to eliminate "dead spots," and supports the health of fish, plants, and beneficial bacteria in aquariums, ponds, or hydroponic systems.