Calcium Granulate Dupla Marin is used for regulating the pH value and hardening the water. Installed downstream of a sulphur nitrate filter , the media nutralises the accumulated acids and acts as a pH buffer. Dupla Marin Calcium Granulate can be used in any hardening filter or calcium reactor. Depending on the CO2 content, a hardness of max. 20 KH can be achieved. Can also be used as a biological filter media and white substrate in nano tanks. Made of 99.6% pure calcium carbonate of organic origin . Consult the filter manufacturers manule when filling the filter with media.