Read this-- Phosphorus exists in two primary forms in seawater: as inorganic phosphates, especially orthophosphate, and as organophosphate forms. Orthophosphate is readily taken up by algae and is active in inhibiting calcification. The organic forms may or may not be available to organisms such as algae. Aquarists can readily test for inorganic orthophosphate using a standard aquarium phosphate test kit, but testing for organic phosphorus compounds is considerably more tedious. Moreover, if there is an algae problem, then the algae may be consuming the orthophosphate as fast as it enters the water, thereby masking the issue. Consequently, many reef aquarists may not recognize that they have a phosphate problem, only that they have an algae problem.
