What kind of water are you using (tap, RO, or distilled)? If using tap water, what is the ppm of the water alone?
Many municipal water sources are heavily buffered to resist ph changes (and help the pipes last longer)
if your water is buffered to 7.0 ph, for instance, all adding acid will do is drop the ph temporarily; the buffer will adjust the ph back to 7.0. If your water ppm is relatively high (say above 200 ppm) it is probably heavily buffered and will resist changes to ph
it will take a lot of ph down to counter the buffer. Try using distilled water or invest in an RO system.