In plants, algae iron acts as a constituent of cytochrome and chlorophyll, as well as act as enzyme systems, and electron transfer in photosynthesis, excessive iron levels greatly inhibit the fixation of other elements (Effendi, 2000). Iron also plays a role in the oxidation-reduction in the process of photosynthesis and respiration in addition to a few enzyme cofactor in plants (Agustina, 2004). Iron deficiency can cause the color of the plants turn yellow or pale (Dwidjosaputro, 1992).
Fe levels which support life seaweed is> 0,018 mg / L (Pratomo and Sulistyowati, 2002). While Moore (1991) in Effendi (2000) adds that when the iron content exceeding 1.0 mg / L are considered harmful to the life of aquatic organisms. So that iron levels are still within the range considered safe for seaweed cultivation ranged from 0.018 to 1.0 mg / L.
Sodium is a necessary micronutrient plant to activate the enzyme nitrate reductase in nitrate utilization by plants (Graham and Wilcox, 2000), while Agustina (2004) mentions that sodium also serves as a regulator of water balance in the plant and able to accumulate oxalic acid. Sodium is needed in the construction of the structure of the cells of the seaweed, also plays a role in the mechanism of electron transport in the metabolic process that occurs between plant cells.
Sodium content of seaweed is needed only in small quantities but have an important role in the growth in the amount of> 0,005 mg / L (Pratomo and Sulistyowati, 2002). Sodium ions in the waters of the high seas has the highest concentration of which reached 10,500 mg / L (Subandriyo, 1986).