I agree with the consensus on not attempting to attempting to have a "perfect" ph, just a stable one. However I do see some confusion on the concept of hardness. What everyone typically refers to as hard water implies GH (general harness). Carbonate harness is measured in Kh and is also referred to as alkalinity. They are not one and the same and not even directly related. When attempting to lower Ph in your water I would start off by measuring Kh. There are several test kits on the market that do that quite well, API being the one I use. Once you determine the alkalinity you can use an acid buffer to lower Kh, while also lowering Ph. However the Ph will still float once in the tank. I have also used almond leaf extract to lower Kh, but it's quite expensive when done with every water change.
