They make stuff that you flush with that will lower your ph, alot quicker than just plain water, let me see if I can remember, the names , Flawless Finish from AdvancedNutrients is one of them, I think Hydrogard is one too, not sure though.
You are so close to harvest, I think you may be ok, I'd you just stay watering at 6.0ph for a while, maybe that will get it back in range.
You needed that flush, ain't no telling what it
would have been if you had checked it before
the flush, alot higher i bet.
Maybe someone else will chime in .
GoodLuck Speedie.