Help.

I have an Ultralife Reef Products pH Monitor and Controller Model
MC-101. I am attempting to convert to the use of this with a Pinpoint
pH probe to turn my CO2 on and off. I had been using the pH monitor
and probe on another tank just to monitor the pH and had been simply
been turning the CO2 on and off with the tank lights via standard
timers and a solenoid.

The problem I have is when the controller attempts to turn the CO2 off
(I suspect on, but the effect is not as bad). When the pH drops to
the point that the CO2 should shut off, the controller "clicks" but
then the reading climbs a few whole points then starts to settle back
down. Once it reaches the cut off point again, the cycle repeats.
So, approaching 6.90 when the trigger to turn off the gas occurs,
controller clicks and then the reading jumps to 8.5 and starts to come
down.....gets back to 6.9 and then repeats. The controller clicks,
but the solenoid never fires.

At first I thought this was a ground issue. I put in a new ground rod
and grounded the tank. No change. I then put the pH probe into a
small container of tank water beside the tank. Same events.

I also note that the pH reading swings when I turn on or off the tank
lights.

So, have I got a bad pH monitor, bad probe or something else? I am
stumped. I suspect the controller is bad and is unable to fire the
solenoid and exibits the bad effects in the ramped up readings.