Provided is a water quality purification material capable of quickly and significantly reducing the concentration of harmful substances in breeding water, such as water-soluble phosphorus components and ammonium ions derived from feed residues, fish and shellfish excrement, and the like, even in a fish and shellfish farm in subtropical regions or the like where the temperature of the breeding water exceeds, e.g., 20°C. A water quality purification material containing granules (A) which have a granularity of 0.01 mm or greater and less than 1.0 mm and contain calcium silicate hydrate as a main component, and porous granules (B) which have a granularity of 1.0-4.0 mm and contain calcium silicate hydrate as a main component, the proportion of the granules (B) in relation to the total amount of the granules (A) and (B) being 10-95 mass%. The granules (B) preferably comprise granules having a void ratio of 50% or greater.
