What kH and gH values does your test kit come up with to give you "hard water" and a pH of 6.8?
Without more information, if you truely have water with "hardness at the top end", presumeably you have using a 'pH down' product/ new unsoaked bogwood/ CO[sub]2 [/sub]system with very fast bubble rate/ almond leaves/ RO water "cut" etc. to get such a low pH?
Southampton's water has 200 /220-240 kH/gH respectively (if a I recall rightly), with a pH of 8.2, which has lowered to ~7.6 with a 30/min bubble rate of CO[sub]2 [/sub]...