1. Dilute your pool water 1:2 with distilled water from Walmart (1 parts pool, 2 parts distilled) and retest pH. If it's still below 6.8, you need tor raise it ASAP. Borax, like Carl suggested, will work. But, if the pH is really low, soda ash (Walmart "washing soda") or pH UP is possibly a better choice.

2. Have you been using trichlor or dichlor to chlorinate? (Like Carl, I'm wondering how you got FC=55 and low pH.)

3. How long has the chlorine been high? If it's been more than a week, and you truly have FC=55 . . . then your CYA must be extraordinarily high. Test the 1:2 dilution for stabilizer, and multiply the result x3.