What is the difference between total dissolved phosphorus and total insoluble phosphorus?
EPA definition of dissolved phosphorus and insoluble phosphorus
Dissolved phosphorus is the fraction of total phosphorus which is dissolved in solution rather than being attached to particles suspended in solution. It is determined by first filtering the sample, then analyzing the filtered sample for total phosphorus. Insoluble phosphorus is calculated by subtracting the dissolved phosphorus result from the total phosphorus result.