I would add 10 lbs of baking soda if you're comfortable with your test results. That Alk of ZERO is beyond my ability to address.

There is a close relationship between pH and Alk, however, and 10 lbs should be adequate to make your Alk (and pH) results move in the correct direction.

Hold on the Borax, put in the Baking Soda, circulate and retest in around 6-12 hours after adding.