Yes, add borax when your pH is low.

BUT, with FC=27, you need to retest your pH using a 1:1 dilution of your pool water with distilled water (gallon jug from Walmart; NOT 'bottled', 'artesian', 'spring' water: DISTILLED). Adding distilled water to your pool water will not change the pH noticeably, but will dilute the chlorine. Very high chlorine levels can convert the phenol red into another indicator, with different colors, leading to invalid results.