dont be afraid to flush, flushing is like cleaning, its no different than 2 days straight rain ...yeah?

and your correcting a little low optimum PH is 6.5 - 6.8 for soil
vinegar is not the best choice for correcting, its works yes, but why not add something benificial to the water instead of something the plants not interested in.

PH down (phosphoric acid based ph down) is the best to use as our plants use large quantities of phosphorus throughout its life cycles

for ph up one should use a potassium based ph corrector as again the plants use large quantities of potassium

making a slurry and testing the PH of it will work fine