I would split up the doses and since you've got gallons of acid you could add one gallon of acid and then 100/6 = 16-2/3 pounds of Borax, then acid again, etc. If you add slowly over a return flow in the deep end, then I would wait 5 minutes between additions which should give a reasonable amount of mixing assuming you've got some decent circulation. Put the pump on high if it's a multi/variable speed pump. Also, be sure to lightly brush the side and bottom after doing each addition to ensure thorough mixing. From the quantities you've given, it sounds like you've got a pool around 27,500 gallons or so, is that right?