:  Phosphate Home  >  Library  >  Phosphate Back Phosphate: 0 to 0.3 mg/L Phosphate (PO43-) is utilized by all cells as an energy carrier between organelles and an information carrier between cells. Phosphate is removed from solution by all photosynthetic algae as they photosynthesize and produce new cells. Free phosphate (PO43-(aq)) is called 'inorganic', while phosphate bound to biochemicals (such as adenosine triphosphate or ATP) is called 'organic'. Phosphate is released into marine aquarium water by the decomposition of organic matter, which simultaneously consumes oxygen. Sources: Phosphates find their way into aquarium systems in several ways: Overfeeding: Too much uneaten food in the aquarium is likely the most significant source of phosphate in the water. Decomposition rapidly releases the organic phosphate as inorganic phosphate. Tap Water: Tap water has phosphates that are often sourced from upstream livestock operations that should never be added to a marine aquarium. Decomposition: Dead organisms, algae or animals, release phosphates into the aquarium water as they are decomposed. Low-Grade Activated Carbon: Phosphoric acid used to etch the pores of activated carbon can end up in the marine aquarium. High-grade activated carbon is more expensive - the acids are removed. Control: While phosphates in sea water are generally around 0.07 mg/L, it is recommended that marine aquarium systems keep the phosphate below 0.05 mg/L. Phosphates can be controlled in an aquarium by either biological or chemical means. Refugiums with high growths of algae and good water flow offer a biological method of phosphate control. Periodic harvesting of the algae continually removes phosphate from the aquarium system. There are also resins and iron reactor systems that can remove phosphate from aquariums systems artificially. These systems generally involve pump water diversion through a tube of resin/powdered iron(III)oxide which reacts with free phosphate. The "cleansed" water is then returned to the aquarium system. Phosphate Absorption: Phosphates are absorbed by living cells as they multiply to cover rocks and gravel. Their presence indicates a possible phosphate issue. If the phosphate level is initially reduced by water changes and chemical filtration, the bacterial and algal populations that once depended on the excess phosphate will begin to die. As they decompose and disintegrate, they release phosphate and reduce the oxygen levels in the pores of the rock where they grew. This phosphate rebound may produce higher phosphate levels than were initially present before action was taken. Several cycles of water changes and aggressive filtration may be necessary to "permanently" reduce the phosphate to acceptable levels. Phosphate Adsorption: Phosphates are also absorbed by rock and substrate in an aquarium, and then leached out after its aqueous levels are reduced. Calcium carbonate has a high affinity for phosphate ions. The more porous the rock/substrate, the more phosphate that can be adsorbed. If phosphates are removed from the aquarium water, the phosphates adsorbed onto rock/substrate will leach into the water, leading to a phosphate rebound. Several cycles of phosphate reduction may be needed to "permanently" bring the phosphate to a reduced level. Adjustment: Phosphates are continually added to an aquarium through feeding. They can be removed by 1) use of calcium hydroxide to precipitate the phosphate from the water, 2) use of a protein skimmer to remove uneaten food and organic material from an aquarium.