Zinc phosphate, like iron phosphate and tricalcium phosphate, is extremely insoluble and its formation is often preventable through the use of a specific phosphate deposit control agent. In order to predict the potential for zinc phosphate precipitation, refer to the zinc phosphate solubility curve below. Use the chart by entering the zinc and orthophosphate concentrations for the water being evaluated. 

The pH at which the lines meet is the pH_s (saturation pH) for zinc phosphate. Therefore, an actual system pH higher than the pH_s would indicate that in the absence of any specific phosphate deposit control agents, zinc phosphate would be likely to precipitate. Therefore, when zinc phosphate precipitation is a potential problem, consult marketing for specific product and dosage recommendations.