The 7 balls are nutrient-rich fertilizing pellets, enhanced through a special process to include essential elements for aquatic plants, particularly iron and trace elements. They release nutrients gradually, creating an effective reservoir effect. Their ball shape allows for easy application in existing freshwater aquariums. Ideal for the targeted nutrient supply or post-fertilization of aquatic plants that primarily absorb nutrients through their roots, such as Echinodorus, Cryptocoryne, and similar species.