Phosphorus

The element phosphorus is essential for all organisms and occurs in the aquarium only as a compound.

The inorganic phosphorus IP is present in the water as phosphate PO₄ and can be assimilated by all autotrophic organisms (plants, algae, zooxanthellae, many bacteria). Another type of inorganic compound is produced when precipitating with lime water. The hydroxyapatite formed, if not removed by filters (skimmers), settles in the bottom and can be released again by bacteria as phosphate (phosphate pools).

Organic phosphorus OP is present in compounds such as phospholipids, phosphoproteins, DNA and ATP. The dissolved forms are summarised as dissolved organic phosphorus DOP, the particulate forms - i.e. also plankton and food - as POP (particular organic phosphorus).

The sum of organic and inorganic phosphorus is called total phosphorus TP. Only this total phosphorus is measured in an ICP analysis. The theoretical conversion factor from phosphorus to phosphate is 3.1 - this calculated value must in any case be greater than the photometrically determined phosphate concentration. In the total phosphorus concentration, organically bound P compounds (DOP = dissolved organic phosphorus and POP = particular organic phosphorus) and inorganic salts (PIP = particular inorganic phosphorus) are also measured.