you mentioned the unit is less than a year old? maybe that probe is done, how did your friend store the probe, had it been out of the tank for a while before it reached your hands? if that's the case it could be no longer any good. you normally get a year give or take out of a probe i've found. now the first thing you need to do is take care of that.
if you're pH is reading 6.8 now, why don't you just adjust your setpoint to 6.7 and see how it goes? the solenoid should open till pH reaches 6.7 then close.
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