Maybe try a flush and then water with water pd'd to 6.5? As long as the ph of everything going into your soil is 6.5 you shldnt have problems unless your soil has ferts in it and they are messing with the ph....I don't check ph of my run off,,,neutral soil, 6.5 in =healthy plants in my book. Now if your soil has ferts in it or is amended then I always hear that lime will help you out..but it won't work quickly.