pH dropping steadily tonight

[Aquattro]

I don't believe those readings. Corals can actually start dissolving below 7.7. I used to have tons of pH problems. Solved them all by throwing away my pH meter. Although it may be a cool gadget, I'm confused why we run them. They may be useful for tuning a Ca reactor, but monitoring pH full time? I now look at my fish and the coral polyps, they tell me how the water is doing.
I don't believe hobbyist meters can accurately measure pH full time for very long without a lot of tinkering and cleaning of probes. When I had my pH problems, I used 4 different calibrated meters, and got 4 different readings. Borrow a meter or buy a cheap test kit to verify the readings you're getting. If you have livestock in there, you should notice odd behaviour at 7.59....