I'm not on NxStage, but...
I had a rare HIGH CONDUCTIVITY alarm the other night. Like most of these rarer occurences, when it happens for real, the only thing to do is to reach for the manual (or whatever you have that is equivalent). First the alarm wakes me up. Then the blood pump stops. I've got to do something before my blood is too old to rinse back. So I quickly scan through the instructions on High Conductivity. Everything looked good. I can't see or hear my R/O in the other room, so I asked my wife to check to see if it was still on. It was. By this time, the conductivity has returned to normal, and so I simply press RESET, and carry on with the treatment. No more problems that night. My best guess is that there was a short interruption in the water supply in my apartment building.
My point is that even though we do go through all the possible alarms in training, some situations are rare enough that by the time it happens at home, you've probably forgotten the exact procedure anyway, so, keep the manual handy.