I have exactly the same issue! Have borates 50 ppm (added granular boric acid), corrected TA also 48 ppm (Taylor testing) and pH high ~7.9 (tested with Taylor and two different stores) Water a month old now but noted this issue within 2 wks of deep cleaning, water change and adjusting all chemistries. Using chlorine (just dichlor).
I think somewhere in this forum (by someone knowledgeable) there was a posting indicating with borates not to be concerned and not to adjust unless above 8.0, but also a bit worried.
Any insight helpful! Thanks.