[Nils A. Seastrand]

Many years ago sodium phosphate NaH2 PO4 (monobasic) was commonly used to shift pH to the acid side,and yes, even vinegar and dilute hydrchloric acid were used as quick, but not very permanent, solutions. In my humble opinion, the closer to natural we can get the better the results.Also, remember that naturally derived acids(eg. tannic) address overall water condition and not just pH. —thanks