In recent years, algae cultivation in the Seto Inland Sea has suffered damage due to low nutrient concentrations, and so there is a need to develop a technology for applying fertilizer with less environmental impact. In this study, a technique was developed to efficiently supply nutrients by filling cylinders with small holes (Kagawa-style fertilizer cylinder) with fertilizer and gradually releasing the dissolved fertilizer solution inside the Pyropia thalli growing-nets, where the flow velocity is slower than that outside. The vigor and color of Pyropia thalli were improved by this new method and the quality of the product was well recognized by the market.