I’ll save you the cell phone minutes (since I have to pay for them) 
40 Tetras of each color. About half on the manual loading station side, about half on the automated loading station side. The intent is to keep both sides of the field in a state of “constant supply” so neither the human players hands nor the automated loading stations are ever empty. The field attendants will attempt to keep an appriximately even distribution of tetras between the two side of the field. Based on the initial esitmates, neither side should ever run out of tetras during the course of a match. If necessary, the field attendants may move some from one side to the other if one side is becomming heavily depleted.