Chem_geek is not wrong, of course. Your T/A is probably 'way too low. But my recommendation for Borax is to get pH into the normal range so you can see what else is going on. Baking Soda's cheap, so is Borax.

But if you do go the soda ash route, Arm&Hammer WASHING Soda is the right stuff (Sodium Carbonate) and even cheaper (in my supermarket) than Borax per pound. The Washing Soda box is Yellow, not orange. It will be in the laundry products section.

Either way should be fine, but you MUST get pH up.