I knew what Zandor was refering to with the vinegar. not by experience but I have read many times vinegar is unstable, and often by the next day ph rises. I avoid ph down and up because of the non-organic thing as harddon pointed out. Rather I just get my soil neutral, use r/o, foliar feed w/ seaweed when necessary for nutes that may bind when ph is not low enough. other than than 6.8-7 is fine for the rest of nutes in soil.