adding borax is really a no brainer. Don't make it into something harder than it really is. Calculate how much you need, add half the amount and half the acid, brush, and add the rest. Wait 48 hours, adjust your pH to 7.6 and test your borate levels. Check them about once a month and when they drop to 30 ppm add enough borax and acid to bring them back up to 50 ppm.