Water clarity is influenced by the abundance of phytoplankton, zooplankton, and suspended soil particles within the water column. Phytoplankton and zooplankton generally do not influence water clarity as significantly as suspended soil particles. "Muddy" water is the result of tiny soil or clay particles suspended in the water from organisms (from example carp) stirring up the pond water, the presence of colloidal clay and/or overland runoff.
Nutrient Control - Phosphorus and nitrogen combined with carbon dioxide are the main culprits responsible for turning your pond from clean to green. All aquatic plants and algae make their own energy through photosynthesis which uses sunlight and carbon dioxide to create energy and oxygen as the byproducts. The other key ingredient to plant growth and health is nutrients, primarily phosphorus and nitrogen. By tying up any existing nutrients in the pond algae and nuisance plant growth can be slowed.