To add or change initial quality and source information for node in a multi-species model, you have to select the specified node, click on the Multi-Species Node Quality button  from the Model Explorer - Attribute Tab. A dialog box as shown below will appear.  

First, you should select the name of the specified model from Define Initial Quality for Model drop-down menu. Then for all the bulk species defined in that model, the initial quality, source type, source strength, and source pattern are allowed to be edited.