pH is one important factor in the life of marine algae, as well as other factors. According to US-EPA (1973) in Iksan (2005) maximum pH range for the life of marine organisms is 6.5 to 8.5. Chapman (1962) in supit (1989) states that almost the entire algal like a pH range of 6.8 to 9.6 so that the pH is not a problem for growth. Furthermore, Kylin (1927) in supit (1989) found resistance scattered algae is at a pH of 3.6 to 10.
But according to Rao and Mehta (1973) in supit (1989), there is a marine algae that require a water pH conditions typical for him. Seaweed or algae as chlorophyll plants require nutrients other as a raw material for photosynthesis. To support the required growth in the availability of nutrients in the waters. The entry of materials or nutrients into the body tissue seaweed is by way of a diffusion process that occurs in all parts of the body surface of the seaweed. When more and more will accelerate the diffusion of metabolic processes that will increase the growth rate. Diffusion process is influenced by environmental factors, especially by the movement of water (Doty and Glenn 1981).
The nutrients needed by plants, including phytoplankton can be grouped into two parts, namely macro-nutrient, required in large quantities and micro nutrients, are needed in very small amounts. Which includes macro nutrients needed by algae is sulfate, potassium, calcium, magnesium, carbon, nitrogen, and phosphorus. Sulfate is required for protein synthesis and production in the form of bond sulfate polysaccharide sulfate (carrageenan).
Potassium as an enzyme activator, magnesium for chlorophyll synthesis, calcium for the formation of cell membranes and cell walls, the carbon to the formation of carbohydrates (carrageenan), nitrogen and phosphorus for plant growth for energy generation and transfer process, while the included micro-nutrients include Fe, Mn, Cu, Si, Zn, Na, Mo, Cl and V (Baracca, 1999 in Iksan, 2005). N and P elements necessary for growth, reproduction and for the establishment of food reserves in the form of the content of organic substances such as carbohydrates proteins and fats.
Needs nutrient seaweed is then boost utilizing seaweed as a biofilter, so that seaweed can also be cultivated farming polyculture with other organisms such as shrimp and fish. Food remains and feces that contain many elements of N and P that can not be utilized by the fish and shrimp will be used by the seaweed as a source of nutrients, so there is no eutrophication in aquatic cultivation besides benefit more from the cultivation of seaweed which can be used directly.