Doc, thanks for taking a look at my sketch. Yes, Have verified the functionality of the Ph stamp using both an Arduino Mega and a USB->serial "debugger that Atlas sells. Because it works fine with the basically the same code on a Mega (different in that my Mega sketch uses hard serial), I suspect that the details of softserial are at the core of my strange problem. I am going to return to the Atlas sample code to see if a single instance of softserial is reliable.
Thanks
Quentin