Oyster shells

In Japan, oyster shells (牡蠣殻 kakigara) have been used for decades in ponds, rice paddies, and medaka containers. The reason is simple chemistry. Oyster shells are mostly calcium carbonate (CaCO₃). When placed in water, they slowly dissolve, nudging the water toward higher hardness (GH) and slightly higher pH.

Medaka evolved in Japanese streams, irrigation canals, and paddies that are often mineral-rich and mildly alkaline, especially compared to ultra-soft rainwater or RO water. Oyster shells act as a buffer, preventing sudden drops in pH and providing minerals needed for healthy physiology.

Please see our advice and care information section for the use of oyster shells in biotopes, aquarium, ponds etc. Click here