Here's a pre-meeting update so you guys can sufficiently deride me...
Yesterday morning I replaced the pH probe with a brand new one. The old one *seemed* to be working when tested against 7 and 10 pH calibration solutions, but it turns out that wasn't the case. How it could be accurate at 7 and 10 but off in the middle will remain a mystery.
Here's the sordid 5-days during this thread. You can see how with the old probe the reading peaked out up above 8.45 where I had the lights turning off for high ph. The saw-tooth patterns are the lights turning off and on for a few hours at the end of the light cycle.
The yellow line is the new probe. Without any calibration, the pH reading adjusted from about 8.15 to 7.85 (!) That was a bit surprising, but I was relieved as the previous behavior shifted down that much would not have been at all concerning.
Being very tired of topping off by hand with fresh water, I decided to turn the kalk top-off back on again. With kalk dripping all day at the evaporation rate, pH topped out at about 8.35 when the lights went out.
At about 3 am I couldn't sleep, so I decided to make sure the new probe was properly calibrated. You can see the calibration where the chart caught one of my tests with the pH 7 solution. The end result was about 0.03 higher as you can see with the little step up in the chart.
As dcforester said, things were fine before I was measuring pH.
And as Steve said, readings above 8.5 are probably bad readings.
Lessons learned...
1. Trust the corals. If they're happy, then parameters are probably good and equipment should be questioned.
2. Trust science. Healthy salt water should just stay in the good pH range unless you're overdosing with something.
3. Don't trust equipment unless you can verify it is correct.
4. I'll be throwing away that old probe and the crappy pH test kit. (Office Space style, with a bat.)
Even though my concern was for nought, I was forced into some research and experimenting that was a great learning experience.
I still want to see if I can lessen the swing. I will probably set things up so that the Kalk top off only happens when the lights are off.
Thanks for all the help. I couldn't have done it without you guys.