Warning to anyone using an electronic PH meter. I thought my tank was seriously screwed up once due to wacked out readings from my meter. Turned out that the lighting system caused electrical interference with the meter. I will only check it now with the lights off! I run 2-175W MH and 4- 110W VHO's.
I myself had a horrible PH plummit over the weekend. Down to 7.6...I was running just fine with Crushed coral sand for about 4 months at about 8.0-8.1 and then Saturday morning, 7.6 !Ouch! I bought a buffer and I'm slowly working it back up. Corals were pretty angry, but thier looking up.
Reefman-
I have had the same problems with my pH monitor. I thought I had some major pH spike and started to worry until I found the real problem being the pH meter itself. So for me, batteries only. And I also clean and calibrate more regularly to help avoid false readings.