Phosphate The "simplest" form of phosphorus in reef aquaria is inorganic orthophosphate (H3PO4, H2PO4-, HPO4--, and PO4--- are all forms of orthophosphate). Orthophosphate is the form of phosphorus that most test kits measure. It is also present in natural seawater, although other forms do exist there as well. Its concentration in seawater varies greatly from place to place, and also with depth and with the time of day. Surface waters are greatly depleted in phosphate relative to deeper waters, due to biological activities in the surface waters that sequester phosphate in organisms. Typical ocean surface phosphate concentrations are very low by reefkeeping standards, sometimes as low as 0.005 ppm. Absent of specific efforts to minimize the phosphate level, it will typically accumulate and rise in reef aquaria. It is introduced mostly with foods, but can also enter with top-off water and in some methods of calcium and alkalinity supplementation. If allowed to rise above natural levels, phosphate can cause two undesirable results. One is inhibition of calcification. That is, it can reduce the rate at which corals and coralline algae can build calcium carbonate skeletons, potentially stunting their growth. Phosphate can also be a limiting nutrient for algae growth. If phosphate is allowed to accumulate, algae growth may become problematic. At concentrations below about 0.03 ppm, the growth rate of many species of phytoplankton depends on the phosphate concentration (assuming that something else is not limiting growth, such as nitrogen or iron). Above this level, the growth rate of many of the ocean's organisms is independent of phosphate concentration (although this relationship is more complicated in a reef aquarium containing iron and/or nitrogen sources such as nitrate above natural levels). So deterring algae growth by controlling phosphate requires keeping phosphate levels quite low. For these reasons, phosphate should be kept below 0.03 ppm. Whether keeping it below 0.01 ppm will yield substantial additional benefits remains to be established, but that is a goal that some aquarists are pursuing with various ways of exporting phosphate. The best ways to maintain low levels of phosphate in normal aquaria are to incorporate some combination of phosphate export mechanisms, such as growing and harvesting macroalgae or other rapidly growing organisms, using foods without excessive phosphate, skimming, using limewater, and using phosphate binding media, especially those that are iron-based (which are always brown or black). Some aquarists have also tried to reduce phosphate by inducing blooms of microorganisms such as bacteria. This last method should, in my opinion, be left to experienced aquarists. Från samma artikel. Man kan använda Rowaphos för att undvika höga halter av fosfat.