Check your pH in the evening... right after your lights go out. My guess is that you're around 8.2 at that time. pH will be naturally lower in the morning, just before the lights come on - and highest at night right after the lights go off. Seeing a 0.2 swing between morning and evening is pretty typical.
For that reason, it's always best to take your pH readings at the same time of day - that way you're comparing apples to apples.
For me, I'm using Reef Crystals, 10% water change weekly, and a salinity of 1.025. After my lights go off, I've never gotten a pH reading of less than 8.1-ish or so. It's normally somewhere between 8.2 and 8.4.
[Edit 1: I'd avoid the pH meter, for now. The thing I see with electronic meters is that people end up chasing pH numbers out to the hundredths decimal place, trying to get "stability". Micromanaging pH is kind of fruitless because if there really is something wrong, buffers will only give you a temporary solution.]
[Edit 2: I'd get a alkalinity test kit and see where your alk
and calcium numbers are at. I'm thinking you might be creeping your ca
parameters out of whack by constantly adding buffer. I know I added buffer during my cycle because I thought my pH was low, and I was fighting my ca
levels for at least a month trying to get them back balanced. Here's a good article in case you need it...http://www.advancedaquarist.com/issues/nov2002/chem.htm