Since you have a vinyl pool Aylad and Watermom are right on the money...get the pH up now.
pH below 7.0 can and will damage vinyl liners.

I think a more important question is how did your pH and TA get as low as it did? Normally that is seen with the use of Trichlor, Dihlor, and or MPS (non chlorine shock) AND not monitoring TA and pH since these acidic chemicals deplete both but since you have no CYA in your water that indicates that you have not used either trichlor or dichlor since they both add CYA to the water and you indicated you shock with sodium hypochlrite (bleach). Do you add acid to your pool and if so do you do it without testing pH?