You said you had hard water though. 6.8 isn't hard. Don't get too hung up on the numbers. None of them need an exact pH number. So what's your natural pH straight out of the tap?
my tap ph is about 6.2, I figured out my problem, when I checked on my fish this morning my Senegal was ripping the fins off the pleco and he died, thats the third fish my senegal has killed that was supposed to be compatible.