pH Controller

I bought an UltraLife pH controller about a month ago.  I notice that when
I turn the tank lights out at night (3 flourescent tubes), the pH reading
will instantly jump from say 6.84 to 7.8 for a second, triggering the CO2
to come on for about  15 to 20 seconds.  Right after the jump, the pH
readout starts  rapidly coming down to where it was before it spiked.  In
the meanwhile though, it needlessly turned the C02 on.  The controller is
in the same outlet as the lights, but on its own power bar.  This is the
second ultralife controller I'm on.  The first one was defective, but
similar happenings, pH readout spiking and turning itself on and off
repeatedly until I pulled the solenoid plug out of it.  We tried putting it
on its own wall outlet, but it still insisted on mysteriously spiking at
odd times and turning itself on for a bit.  Anyone have a clue to whats
happening here, or better yet, a suggestion? This didn't happen in the
first week of use.

Thanks, Kelly

"Candle?  What candle?  I don't see any candle, it's too damn dark in here!"