As we discussed already of this manual, zinc tends to form a zinc hydroxide precipitate at system pH of 8.0 and above. However, there are specific zinc stabilizers available that can maintain zinc in solution at system pH's as high as 8.5 and above. 

Consult the zinc hydroxide solubility chart below, to determine if zinc hydroxide precipitation is a potential problem in a given water. Please note however that the chart does not account for the presence of specific zinc stabilizers.