Aquarium fertilizer containing phosphorus easily assimilated by plants. Phosphorus is one of the macroelements vital for proper plant life. This element constitutes the building block of substances such as: nucleic acids, proteins and phospholipids, thus is involved in life processes of plants playing an important role in biochemical transformations and energy-carrying processes. Deficiencies in phosphorus may occur in purely planted aquariums or in fish tanks with very low stocking density, which is visible in the form of unnatural plant discoloration, deformation of new leaves and dieback of older ones.